Aw, please cut the macho PUA BS, I think it is a poor advice to offer at this point, perhaps later when the situation has settled down. Just because one girl has been unfaithful, it does not mean that every girl is, and will be. The true manly man chooses his girl carefully, sticks to her, and gives her those raging orgasms so that she won't need to get them from elsewhere.
If she is truly sorry, if she truly understands how you feel, and if she is truly willing (from her own heart, not just to avoid retribution or to keep you) to change her ways, and if you are 100% sure of that, I see no reason why you should not take her back. However, if she treats you with disrespect, then let her go, but don't lose faith and pick your girl more carefully the next time.
-SS (Mood 2)