WMG / It's (Not) Your Fault

Sam was sexually abused by her father.

This would help tie up some loose ends of the plot. For example, why does Luna have such a strong suspicion that Sam is attracted to Lincoln? Is it just because Luna is too stressed trying to write songs for her band on short notice before the contest? Or has Sam confided to Luna that her father abused her, and Luna is afraid that Sam abuses Lincoln too? In that case, Luna would not be merely jealous, but legitimately concerned about not letting anyone hurt her dear brother.

It's worth noting that Sam still has an immense affection for her father, and she never blames him for abandoning the family (in fact, she doesn't blame anyone). Is it possible Sam's mother found out that her husband was abusing her and that was the real reason they divorced? If so, it would make Sam an Unreliable Narrator when she tells Lincoln about her sad past^note Of course, one might question why her mother didn't just report her father to the police and have him arrested, but as the #MeToo movement has demonstrated, reporting a sex offender can be pretty difficult, even more so when the aggressor is very close to you and has power over a good part of your life.

On page 130, as Sam is about to consummate the act, Lincoln makes one last plea for her to stop. But Sam is really obsessed with Lincoln (it's not sincere love, since she's drunk) and says that even if everything is cleared up and she is exonerated, it won't bring her father back. Then she rapes Lincoln. It's pretty clear that she has a strong obsession with her father, and that she abuses Lincoln to fill the big hole left by her father's absence. It's as if having sex with Lincoln could rescue the pleasure she felt in having sex with her own father.