It seems like you both are in a bad place. Move on, cry, go through the anguish and when you are done feeling bad, and your heart starts to heal you will feel better that you did. I don't see how you could forgive such a thing. I have always hated it when someone says "I got drunk and I didn't know what I was doing." How about yes, yes you did know what you were doing because I have been nearly black out drunk and if I didn't want to have sex with someone I didn't and never have. The only way I would believe something like that is if someone told me I had sex with someone and I couldn't remember doing it or let alone anything else that happened after the last drink I had, I would be terrified, that would have meant I was drugged and I doubt that this was the case for her. You need to step away from the rose colored glasses and look at this in a different light, sure what you did wasn't as bad, but you know what, like Michelle said, you probably wouldn't have even done that if she hadn't screwed some other guy before. Move on, there is a girl out there who will never treat you that way and deserves to be loved and respected. I also guarantee she will have the sense to say no if she ever ends up the in the same circumstance. They exist, I am living proof of that. So cry, get it out of your system, and learn to forgive yourself instead of someone else.
“I was never really insane except upon occasions when my heart was touched.” ― Edgar Allan Poe
Wish for a pile of shit to turn into gold hard enough and guess what? It's still a heaping pile of shit.