So I kind of understand the MC's problems (more so than in the last chapter), but at the same time, they annoy me to no end.
Yes, you started going out with her because she asked you and looked incredibly cute, and that's it. So what? I don't mean to criticize the writer here; this is unfortunately an accurate portrayal of many guys/girls his age who seem to mistake dating with getting married. The level of commitment is nowhere near the same, so why not give it a try? You can't just go out only with who you consider the love of your life, for crying out loud; otherwise you might never find that love of your life to begin with.
Also, yeah, the molester game was likely not the best choice ever. But you are her boyfriend, not her daddy, her guardian or whatever. It's up to her to say if she wants to do something or not. It's actually possible (if less likely) that she's already over that incident as far as she is concerned, and does not mind playing the game one bit. You not only beat yourself up for something that isn't your fault, but you actually degrade your girlfriend by treating her as someone you need to make decisions for, instead of seeing her as your equal.