When you come to the realization that your girlfriend is carrying on an affair outside of your relationship... it can be a lot to deal with. You have all of these different emotions that come up and you might not know how to process them. One minute you want to have NOTHING to do with her at all, and the next... you just want to stop your girlfriend from cheating on you so that you can work to repair the relationship.
Sometimes, cheating can be a sure sign that the relationship is over, or that there is no point in living a lie and that the two of you should breakup. And, there are other times when a cheating girlfriend just means that you need to work on repairing and salvaging things, because you don't want to let her get away from you.
Here are some ways that you can stop your girlfriend from cheating on you:
1) Let her know that you know without blowing up out of anger.
Okay, it's only natural that you are going to feel a little angry and a little bit betrayed by your girlfriend's infidelity. When you confront your girlfriend about her cheating, you don't want to let that anger get the best of you, not if you want to repair the relationship and work on rebuilding things so that the two of you stay together and you don't have to worry about her straying from you again.
2) Work on making yourself more available to her.
Many instances of a female cheating are due to the fact that she is feeling an emotional disconnection in the relationship.
3) Make a stand and let her know that you will let her slide this time, but never again.
You don't want to have your girlfriend see you as being a doormat, a guy that she can creep on and he will always just forgive her and take her back. If you really want to make sure that she is not tempted to stray from the relationship again, then you NEED to let her know that this is the last time, or else you WILL walk away, no matter how painful it might be to you.