my girl friend cheated on me and told me about it, do I break up with her, or forgive her?
Depends on how you feel about her. If you really like her then give her another chance, but know that it might happen again. If you resent her for cheating on you, then it might be better to just move on.
I've been w/ her for 4 years and she's cheated 3 times now... I don't know something tells me to move on butim lost w/o her