It is also interesting that the story of Sheen and Haim on the set of Lucas wasn't too far from the movie story, minus the molestation.
In the movie, Haim played a nerdy high school freshman ("Lucas") who was picked on by older kids in school, but protected by an upperclassman football player ("Cappie"), played by Sheen. In the movie you get to witness the quiet admiration Lucas had for Cappie, even when he became jealous of Cappie's relationship with the girl he had a crush on.
In real life, Haim also admired the older and more famous Charlie Sheen, which probably led to him being vulnerable to Sheen's advances. The fact that Haim himself was gay also made it easier. If you doubt this, and you're heterosexual, picture yourself as a 13-year-old and an attractive 19-year-old girl puts the moves on you. Would you have turned that down? I doubt it.
I do wonder if the story line of the movie, which Haim and Sheen had to act out repeatedly over many takes, somewhat contributed to Haim's willingness to have sex with Charlie.
On an unrelated note, one thing that bothered me about the plot of Lucas was the fact that Lucas had a quirky, somewhat attractive female friend who was clearly into him, but he ignored her to chase after an unattainable, pretty older girl. We were supposed to feel bad for Lucas and his plight of not being attractive to the object of his affection, but I just saw him as a shallow jerk who made himself into a victim.