P R O B L E M A T I C
The story revolved around a boy who turns 18 at the beginning of book, and an older man. How much older? It's unclear, and I will get to that in a bit. The protagonists are effectively members of a band/cult. The main character comes from one band, and the older man from another. In the previous book the older man took a liking to the Main character (while he was 17,) and spent time in intimate contact. At the time it was a bit odd, but now it's clear that it was grooming. It's important to point out that there is a vast power imbalance between the two. The older man is one of the most famous people in the galaxy, and the Main Character is just starting out, not sure if they will succeed as a performer. The Older man decides that he wants sexual contact with the Main Character and forces it. The main Character doesn't want it, but feels like he has no choice because the older man has so much power he will get his way in the end, so he aquesses. We have a word for that kind of behavior that I won't use here.
I have not used the characters names purposefully, because I don't want the power imbalance to masked by familiarity. So, how much older is older man? It's hard to say, because the books have two versions of this answer. Often when Older Man's band is discussed, its shown to have been a band for a long time, pointing out how when they started things were different, or talk about how many tours they have done. One of the members of the band is ill. Illness doesn't have to indicate age, but there is a correlation. But when the author talks about an age directly it's much younger, something like only five years. five years isn't enough time to get the fame and power Older Man has, especially by the universes own rules. How do I account for this? Easy, its retcon. I think That the author wrote the book with Older Man as a much older man, top of his power and experienced. But then some editor, or other advanced copy reader pointed out that sexual contact between a barely 18 year old and a 50 something was gross. So some lines were scribbled in about Older Man only being a few years older, and maybe a few lines were deleted. Other lines were not deleted however, and if you pay attention you can see what I feel was authors original intent. And it IS gross. The fact that it looks like the author tried to change the situation means they knew what the wrote was wrong, but they published anyway. Remember this book is tagged as Young Adult. I have no idea why anyone let this book get that tag when it portrays SA as it does. Nobody publishes a book by accident, a lot of people were involved in this, and shame on each and every one of them.
TL;DR Previous book grooms 17-18 year old for sexual assault encounter with vastly older person, which happens in this book. Textual evidence suggests author tried to mitigate the horror, meaning they did it on purpose.