OK I'll try (fail) to keep this short.
I have been going out with this girl for 3.5 years. Started going out when we were 16, fairytale romance and all that. We went to different universities but kept the LDR thing going. For two years this seemed to be fine, and we saw each other every two or three weeks at most. However the last year has been very intense on both of us and we rarely saw each other. Possibly as a result of this, she cheated (read: slept) with friend of hers (who is a complete *******, and she knows it). I was incredibly angry at this and finished things with her. But there are still a lot of feelings there and when, in a moment of weakness, I asked her to come to a Ball-type-thing at my uni,she quickly accepted.
This event happened last weekend, and we got on really well, just like we were a couple again for the most part. I found out that she had started sleeping with the *******-friend of hers. She says they aren't really "going out" and that she doesn't care about anyone else but me and that "the last few months haven't seemed real". Still, this news made me feel pretty sick.
Well whilst she was down here we hooked up, of course. I don't know what her motives were for doing this. Part of me is disgusted at her, thinking that she is no longer my sweet little angel but just some slut being bounced around between different guys. On the other hand, she did geniunely seem apologetic and upset about everything and says she wishes she'd never done anything with anyone else. Her parting words (through a mask of sobs and tears) were "I promise I'm going to get you back".
Right you know the obvious questions. Anyone been in a similar situation? Am I crazy for even considering her? Can I ever trust her again? Advice, perspectives appreciated.