Forbidden Variables

by S.B. Vale

Some things are predictable.
Measured.
Contained.
Understood.
This isn’t one of them.
Ana and James weren’t looking for anything.
They already had everything they were supposed to want — careers, families, lives carefully built over years.
Then one delayed flight changes everything.
What begins as instant chemistry becomes something far more a connection neither of them can explain or ignore. Drawn together by sharp wit, late-night conversations, music, and the terrifying feeling of being truly seen, they find themselves crossing lines they never thought they would approach.
Because some things refuse to stay rational.
Not the pull between them.
Not the way they understand each other without trying.
Not how quickly it becomes impossible to walk away.
It isn’t simple.
It isn’t right.
And it may cost them everything.
But sometimes the things you’re meant to resist are the very things that make you feel alive again.

279 pages, Kindle Edition

Published June 23, 2026

Reviews

[Sinny]

I didn’t expect to love this messy story as much as I did. I was giggling and kicking my feet one second and then crying the next. It just hit me in the feels and I absolutely devoured this book.

I love how it shows how messy life can be. How we settle into routines and just let life pass along without actually living it. I did not expect to root for the cheaters, but they had me from the moment they met.

Absolutely worth reading if you want a romance with adult characters with life experiences making morally messy life choices. Ana and James were both very likeable characters and you will end up rooting for them even when it’s morally wrong.

[Rosie]

I absolutely devoured Forbidden Variables. I picked it up and basically didn’t put it down until I was finished. And I mean that literally…there is now enchilada sauce on the pages because apparently putting the book down long enough to eat dinner was asking too much. I’ll be completely honest: the cheating trope is normally a hard sell for me, and if I hadn’t already wanted to read this author, I probably would have passed on this book based on that alone. I don’t condone cheating, and neither does this story. That’s actually one of the things I appreciated most about how S.B. Vale handled it. The story never asks the reader to justify what these characters do. Instead, it shows us how they got there. This is the story of two imperfect people, the choices we make, why we make them, and the very real consequences that follow. I didn’t always agree with their decisions, but I could understand them. And there’s a huge difference between understanding a character’s choices and condoning them. And in the middle of all that messiness, she gave me a romance I was completely invested in. The tension. The longing. The chemistry. THE YEARNING. So good. Somehow, she made me root for a romance I went into thinking I might not be able to root for at all. These characters felt real because they were flawed. Relationships are complicated. People are complicated. Sometimes there isn’t a convenient villain to blame, and I loved that this story allowed its characters to be messy without asking the reader to excuse their behavior. I even enjoyed the characters I wasn’t necessarily supposed to love, the kind you want to shake while also admitting you understand exactly why they are the way they are. And I have to mention the little extras! I loved the playlist, and including the actual knitting instructions for the hat she makes him was such a sweet, personal touch. Messy, emotional, complicated, romantic, and incredibly human. Well worth the read.

[Heather Joyce]

Wow! This book was extremelyyyyy good and well written! Even with cheating as the main trope, it hit for me.

First I would just like to say how much I appreciate the care the author took with the topic of child loss, that’s literally the only thing in a book that will trigger me because it’s something I’ve unfortunately experienced. But what helped even more was the authors relation to the subject, it was something she had also unfortunately experienced herself. She handled it thoughtfully, didn’t go into too many details, but enough you understood what happened. For once I wasn’t left crying reading this or like I wanted to close the book and not keep going.

With that being said, it made Ana feel very relatable for me from that point on. The sadness she felt, the grief, the loss of herself. I felt that in my soul.

I honestly couldn’t read this story fast enough. The instant chemistry between James and Ana felt electric even as the reader.

Mark sucked, flat out. If how he handled Elodie wasn’t enough, or how he treated Ana around his mom, Mother’s Day was just atrocious. I wanted to slap him so many times. I was thankful he didn’t make their separation more of an issue, Ana deserved a clean break.

James? Yeah fucking loved him, all of him, every line about him in the page, every word he spoke, LOVED. Emma, girl, we all knew from the beginning what was going on…

With cheating being the main trope of this book, I knew it would be messy and it was. But in a page turning way. I never knew how anything was going to play out at any point in the book, which kept my interest and the anticipation high! The twist at the end, didn’t see coming but it was a complication that honestly I felt like made Ana really see so much about herself, her life and her choices. I was SO happy when she finally told mark what she wanted.

[Mrs Marston]

I absolutely loved this book. I never thought I’d read a book about infidelity (something I completely disagree with) and somehow find myself rooting for the cheaters!

I don’t want to say too much because I don’t want to accidentally spoil anything, but this really is a book for everyone. The yearning between two strangers, the complacency that can creep into a marriage, learning to stand up for your own wants and needs… this book has it all. I genuinely can’t wait to see where everyone lands on the moral side of this story after they’ve read it.

The honesty and realism in S.B. Vale’s writing had me completely hooked and even questioning my own moral compass! This is my second book by her, and I can honestly say I can’t wait for the next one. As someone who mainly reads fantasy, her books somehow bring me back to reality while still leaving me smiling and feeling completely fulfilled in ways I never expect. She’s very quickly become one of my auto-buy authors. Once again a 5 star read.

[Cozy Vibez]

I really enjoyed this book! It kept me hooked from beginning to end, and I never once felt bored or like I had to push myself to keep reading.

Normally, I’m not a fan of the cheating trope at all, so I wasn’t sure how I was going to feel about this story going into it. But this book genuinely surprised me and managed to make me enjoy a trope I would usually avoid.

One of the things I appreciated most was the pacing. Everything unfolded naturally, it was never too slow or too rushed, and there was always enough time to breathe between scenes without losing momentum.

Maaaaybe, and I mean maaaaybe, I would’ve made the spicy scenes a little spicier. But honestly, that’s probably just the dark romance reader in me coming out.

Overall, this was such an enjoyable read. The story flowed really well, kept my attention the whole way through, and was incredibly easy to get lost in. I had a genuinely good time reading it!

[Katie Worth]

This is the book I've been waiting for to cure my book slump. I was getting fed up of reading books that overuse descriptions and similes like their readers and their life depend on it. (See what I did there?)

This book is intelligent, witty, and well paced. It has just the right balance of humour, spice, yearning and dealing with past trauma without going over the top or overdoing any of it.

The spark between the main characters was spot on from the start and as someone who has lived both sides of the MCs respective marriages. I get it. All of it.

The correlation of the storyline and the analogy of the bacterial growth curve was chef's kiss. It was woven into the story progression in a clever way.

I will definitely be revisiting this book in the future.

[FeralForFiction]

She's done it again! 🤌🏻🖤

Another incredible book by S.B. Vale! This came out today and I downloaded it as soon as I woke up 1. Because of the hype from her ARC readers and SB herself and 2. Because of how much I enjoyed her other work and I have struggled to put it down all day! The thought she has clearly put into this book is insane, without giving anything away, there's some clever stuff in here! I'm genuinely in awe of her as an author and I cannot wait to read all of her future work.
As usual, check your triggers but I highly recommend reading 🖤

[Sam’s library]

Get this book on your radar it will make you question your morals and connection with the FMC, feeling unseen in a relationship that has gotten “comfortable” with work, children and general life admin the FMC finds a connection when she wasn’t looking but couldn’t ignore the signs. I definitely recommend this spicy book with a lovely story. This is the second S.B.Vale book I’ve read and they are both equally brilliant. Easy to read dual POV, short chapters and spice, what more can you need from a book.

[Violet]

Wow. Wow wow wow. I knew I was going to enjoy this book, because I loved her first one, but I had no idea just how much it would come to mean to me. From being in stagnant, boring marriages to finding someone who makes you feel alive every single day is an absolute feat. James should be who every woman aspires to find in a partner; someone who sees you, all of you, and not only supports it, but encourages it. Ana was so strong when she finally left Mark, but I honestly wanted to reach through the screen of my Kindle and shake her when she stayed, just because of the accident. All in all, if I could read this for the first time again, I would.

[Jane Harmon]

Forbidden Variables by S.B. Vale isn’t just a contemporary romance—it makes you question everything you think you know about love, loyalty, and marriage.

What if the person you’re with isn’t the right person? What if you’ve spent years living the life everyone expects, but deep down you don’t feel seen, valued, or truly happy?

Would you leave?
Would you stay?
Or would you cross a line society says you never should?

This book had me asking myself some uncomfortable questions. Personally, I believe everyone deserves to feel loved, appreciated, and fulfilled. If a relationship has become nothing more than going through the motions because it’s what’s expected, then maybe the bigger question isn’t “Would you cheat?” but “Why are you staying?”

Some people will absolutely disagree with that, and that’s okay. That’s what makes this book so compelling—it sparks conversations that don’t have easy answers.

If you’re looking for a romance that is emotional, thought-provoking, and guaranteed to have you questioning your own beliefs, Forbidden Variables is one I highly recommend.

[Alexandra Rose]

✨Summary✨
Rating: ⭐️⭐️⭐️⭐️.5
Spice: 🌶️🌶️🌶️.75
HEA: Yes, 3rd act breakup
POV: Dual
Tropes: Taboo, Married (to others), Affair, Industry Peers, Instant Attraction

Ana and James meet at the airport while waiting for a delayed flight to a science conference they are both attending, and the attraction is immediate. There’s only one issue…they are both married to other people. Neither is happy in their marriage, but they’ve both tried to make things work for the sake of their kids, and neither has ever been tempted to cheat before. They try to keep their distance, but over the course of the conference they keep finding themselves drawn back together until one night they finally stop fighting it. That night begins a months-long affair, mostly carried out through phone calls and messages with only a handful of stolen moments together since they live in different towns. Just when they start to think maybe they could leave their marriages and take a chance on each other, an accident happens that causes one of them to rethink everything. Will there ever be a chance for their love to exist outside the shadows?

First off, it’s very important that I mention this book involves cheating, but only on their spouses, never on each other. I know that’s a hard limit for a lot of readers, and cheating is usually a hard sell for me too, but I thought this book handled it incredibly well. There was so much emotion between Ana and James, and neither of them is cavalier about what they’re doing. They both struggle with the guilt of cheating and the potential consequences for their families.

Over the 9-10 months of their affair, they only meet up a few times, with most of their relationship happening over the phone. James’s wife is completely disconnected from their marriage and seems to treat James more like a roommate. Ana’s husband is a little easier to dislike and root against. He doesn’t really see or listen to Ana and seems to care more about his mother’s feelings than hers. He doesn’t even get Ana a Mother’s Day present from the kids but makes sure to get something for his own mom.

Trigger warning: There is also mention of stillbirth. Ana is still deeply grieving the loss, while her husband doesn’t want her to talk about it because he finds it depressing. To me, that seemed to be at the root of so much of the distance between them.

It feels strange to say when we’re talking about two people cheating on their spouses, but Ana and James really did feel made for each other. They see and understand each other in ways their spouses haven’t in a long time, and they genuinely bring out the best in one another. Their relationship felt much more emotional than physical, and somewhere along the way I stopped thinking “you two should not be doing this” and started desperately wanting them to figure out how they could actually be together.

[Hell of a book (Helga)]

Morally messy, forbidden love, yearning and boundaries that shouldn’t be crossed. Although you do start to doubt that last part.

This book is about 2 scientist that meet at an airport. Instant chemistry. The universe puts them together again and again turning the instant chemistry into a connection neither of them wanted. Not because they don’t want love. But because they were supposed to have already found their happily ever after.

This book is about life. Its raw and seldom easy and clean. Its about marriages slowly turning into joined calendars and boiler appointments. About feeling like somewhere along the way you became a habit. A convenience. Something that was there all along. Until someone comes along that shows you what its like to be seen again.

This book surprised me a lot. Mostly because I would never in a million years thought I would be rooting for two married people to get together. Its definitely morally messy! I loved the characters. I fell in love with Ana and James and I felt for them. And I hated Mark with a passion. All i can say is "Mothersday".. Really?
This book is so much more than just a book about two people cheating. Its emotional, full of curveballs and real life situations. Its mature, funny but also emotionally layered.

This is the second book I have read by this author. The first being FAFO. And I loved both but this one did go to the number one spot for me.

This book does contain spice and also check your triggers. On a scale from 1-10 I gave this a 9!

[Vanessa]

I never thought I would love a book with a cheating trope but this book completely changed that. Ana and James’s journey was messy and real and I loved every second of it. You could feel the yearning coming off the pages as the reader and any book that can make me feel such strong emotions from the writing is an absolute 5 star.

James was just perfect! This is my second book read by the author and S.B. knows how to write a great mmc. James showed up for Ana and understood her in ways that she needed. And the playlist he made her, my heart melted! I’m a sucker for a meaningful playlist and he took so much time and effort to make it perfect for her.

I was so proud that Ana finally stood up for what she deserved and recognized that she deserved more. I was so angry for her on Mother’s Day and hated how that must have made her feel. She deserved so much more than what Mark gave her.

I also really loved how both Ana and James understood what the other needed in little moments, whether that was some encouraging comments on a paper or simply by being there through the panic. I cannot recommend this book enough and I can’t wait to read more from the author!

[Harper N]

I read this book in two sittings because I was desperate to know whether there would be a happily ever after for the main characters or not.

Forbidden Variables was such an easy read due to it being so well written. I really enjoyed the humour, the science, and the music references (the playlist and knitting pattern were such a lush touch), as well as the storyline and characters.

I felt for the main characters and the tough decisions and situations they faced.
This book shows that life can be messy and full of curveballs - The loneliness that can easily occur in a marriage was portrayed brilliantly, as were other topics that can be difficult to discuss.

S.B. Vale is a fantastic writer who really brought the story and the characters to life in the most beautiful way.

100% recommend and can't wait to see what she does next!

[Megan Earnest]

This book captivated me right away, and I held on the for the entire ride. 😉
The plot had me so impressed, and completely invested. I laughed out loud from chapter one and all through. The banter had me blushing hard, and the tension 🥵 had me gripping my phone until 2 am. I needed to know what happend.
Two characters meet in an airport where drinks flow, and turbulence makes for one intesne bumpy ride. This slow burn romance had some intensity off the plane than on it, and I was not prepared. This story was such an easy read, and I enjoyed every second. ♥️ can't wait for more from this author!
If you love:
We shouldn't be doing this
Cheating trope (done right)
He falls first
Spicy ❤️‍🔥
Sloooooow burn
This is for YOU 😘

[Katie]

This book felt like such a wild card - I was not expecting to feel the way I did, especially so early on on the book.

S.B has a unique way of telling a story that has you completely immersed and ends up making you question your morals.
The yearning in this book was some of the best I've ever read, the structure and pacing of the writing only added to the gut achingly raw desolation.
I loved that the author stayed true to real human emotion and circumstance, it's messy and it's immoral, but why did it feel so right?

I will forever rave about this book, if you're looking for a book that will set your compass spinning and have you questioning what you thought was right - THIS IS IT!

[RabbitReads_2025]

This book really took me by surprise as the main plot is something I said I wouldn't be interested in. Well I certainly got proven wrong on that one.
After meeting at an airport the chemistry between the leading characters is undeniable, however they are both married and know they absolutely shouldn't want what is so glaringly obvious to them. The yearning and the sexual tension between these two is off the charts and I could not put it down.

Absolutely a five star read for me and I look forward to reading more from the author.

[Char x]

Wow, this book was just wow.. I couldn’t put it down, I enjoyed it so so much. I resonated hard with this book, as I have had an experience very similar in regard to the plot of the book. The playlist was the cherry on top of the cake, listened continuously and on repeat while reading the book. This book was everything, I couldn’t turn the page quicker, read it in any given opportunity, thank you for writing such an amazing book
SB! 💜💜

[Lou McCue]

I loved this book, for me it ticked it all the boxes for a good romance read - spicy, characters with actual depth and an interesting storyline - which in this case is the controversial topic of cheating. It's well written with a great pace and clever in that I had to keep checking in on myself....'I really want them to get together....but they're married!!'

[Makayla cox]

A book full of love, connection, secrets and freedom. A book that teaches you that you do not need or obligated to settle for the bottom. I enjoyed this book and rated it a 5 stars. I recommend this book especially if you like quick chapters!!

[Someone]

I did not think I would be rooting for the cheaters but I definitely was. I loved that Ana was no longer willing to settle for comfortable. This book also got me out of my reading slump 🥰