[James]

I don't know who you are, nor what proms are really like. But if they're anything like TV leads me to believe, your ex sexed this girl up in a hotel room after the prom.

But it is your fault. If he wasn't happy enough with you to be honest with you, it's because there is something wrong with you. I would go back to him, and do whatever he wants of you in order to make the relationship work, if you really do care about him.