UPDATE
Rating: 2.75/5
So, I changed my rating and that's because from that time, I realized that this is can be considered novella. It may be weird, but when I considered in the terms of "full length book, that was still too short" my opinion was more simple and favorable.
In that light, I simply tought this book was too short for my liking and it was frustrating, but I've read short books, that were just as frustrating (if nor more) and enjoyed them less.
However, in light of this being a novella... Well, it just doesn't work as one.
The way I see it, novellas are stories whose plot is substantial enough to hold a story together while simultaneously being too simple to fuel full length books. And the relationship and their development still result satisfactory and complete so that it doesn't require a full length book (unless, of course, it's just a prequel or part of a series centered on the same characters/couple).
And to put it simply, this book just doesn't work as a novella. It has too many aspects,if not everything, that would require more attention (plot, development of the characters, of the couple, of the relationships with the secondary characters...etc...).
And if I compare it to other novellas I read, it just crumbles in comparison.
Sure, usually, whenever I read a novella it's by an author I already enjoy/love and it's part of a series of full length books. But, they still end up being satisfactory on their own and, most of all, I NEVER feel like they should be longer.
I think that, the moment you feel like a novella is too short, to the point that it require the length of a full book, then it's just a failure because, to begin with, it should never have been a novella. It may be wrong, but I just feel like it's a much bigger mistake than having a rushed full length book.
To put it simply, this book just can't stand as a novella. It would require at least 100 pages more.
With this in mind, I would lower my rating to 2, but I also feel like it's too much of a jump compared to my previous rating (3.25/5).
So, final rating 2.75/5