Do not communicate some time with the girl, though if you have already decided to return after infidelity, it is likely that this period of mutual silence has passed. During this period (duration you can define yourself, or rather, your heart itself will tell you how much you need to remain silent) you have to think about good things, to look deep inside himself to understand what you really need. How many pairs - so many situations, and your so unique. You can be sure that cheating girls don't killed your love for her - or, conversely, what you experience has no feelings.
In any case, do not rush things. Blame it, not you, and in any case it should come to you by itself. If you begin to act yourself, you will bring her back, will love still, and not showing her what pain she caused you, she'll understand that can continue to change. You need to punish her, but don't get the word "punishment" a little too literally, not tough measures, namely, the neglect on your side, your silence will be a real punishment if she really loves you and only stumbled. When you see that she repents, to forgive you it will be much easier.
When anger, resentment, despair will pass away, when you are able without pain to look at what happened, it is possible to establish with a girl contact. Just talk to her like a friend - because if the love is gone, why not a friendship? Remember how it all began, for a while forget what it was then. If you are for some time together, then you probably have a lot of common interests, shared good memories of the trip. If you really want to forgive the girl, think about it. Do not try to revive the former respect and love (maybe love is anything left, but she certainly gained some new shade), stay old friends.
Now you need to decide yourself: how exactly you want to forgive your mate. Whether you want to see it again was with you as your favorite, or you can simply friendship? For anybody not a secret that the love - feeling much more vulnerable than a friendly affection. If you understand that the betrayal was for love, that is your girl, not daring to break the relationship with you, loves the other, then it might be better to let her go in peace, and forgive as a human being? Will you remain friends or leave forever - it just depends on the two of you. If you want it back, you will have much more carefully to work through their feelings.
If you decide to forgive your girlfriend after she cheated on you, think about how you behave and how you treat it. Infidelity does not occur in a vacuum, everything has its cause and effect. Gently loving you girl don't climb into bed with another person. Therefore, carefully analyze the situation from different sides, taking into account the peculiarities of your nature, and nature girl. Cheating (if she actually was, maybe the girl just hex) is a worrying sign, and think here it is necessary for both partners.