Problems

[Pygmalion]

Hey everyone, haven't been around for a while, but I REALLY need some help:

Ok. For almost a year I've been with my girlfriend, coincidentally for almost a year I've also been pretty screwed up ie: not eating, getting really depressed, cutting myself, that sort of thing.
So I'm in the middle of my final exams which determine whether or not I get into the university I want, and my girlfriend decides to tell me she cheated on me three times last weekend-blaming it on alcohol which I can sort of understand-but she wasn't going to tell me. She only told me because she was drunk when she was talking to me. Well as you could probably expect, I felt REALLY brilliant. We've been fighting on and off for about a week-during which I didn't do much study-and in every fight she manages to turn everything round and make ME feel guilty! Eg: "its your fault I gave Steve a handjob because you tuned off your phone."
After many tearful conversations with various friends I still don't have an answer. I cut myself more than usual and haven't eaten in 2 days, but I can't bring myself to break up with her. I know she manipulates me and makes me feel like shit, but i have a bizarre emotional attachment. I told her I trust her this weekend (more drunken nights out) but...
What do I do?