What do you do if your girlfriend is cheating on you?
First off, you should make sure that she is cheating. Don't mess
up something unless you are positive that she is indeed cheating.
Next, you should confront her if you are positive that she is, and
the rest is up to you. Do you think you can trust her not to do it
again? Do you love her enough to overlook the mistake? It's all on
you, there is no set way to say what to do.