Dump her. She didn't respect you enough not to cheat and if you forgive her, she will make your life a living hell and she will probably cheat on you somemore because she will lose ALL respect for you, and probably will dump you too. So dump her. You will feel so much better about yourself if you dump her and show her you don't take that crap. Also, be prepared for her to make it seem like your fault that she cheated. Like, "You weren't there for me emotionally", or some bs like that. And, if she says she was drunk, don't listen to her. It's just an excuse. I know what I am doing when I am drunk.