Worst thing about The Perks of Being a Wallflower

I liked the movie as a whole, but I just didn't appreciate the aunt thing. I understand that molestation is terrible, and I think its horrible scars deserve to be explored in film. But what I don't get, or at least what the film didn't explain to me, is how Charlie really felt about his aunt. She was his favorite person in the world, but he also thought she was completely insane. He was consumed with guilt over her death despite the terrible things she did to him. Not to mention that, as a high schooler, he still somewhat believed he was responsible for her death. Come on, he was a smart kid and that's nonsense. If Charlie was severely mentally ill, that's one thing and I could accept his contradictory and irrational beliefs. But that's not the way he's presented. The film presents Charlie's mental breakdown as just an after-effect of repressing memories of molestation. It even suggests that he's well on his way to getting better after talking about it. I don't know if I buy that. I felt like there wasn't enough in the movie to get a good grip of how Charlie really felt about his aunt and that just made the whole subplot a little hard to believe for me.

Maybe someone else could explain what I'm missing. I'd appreciate any response.