She has to take FULL responsibility for her affair, be remorseful for it, sincerely apologize, admit that it's NOT YOUR FAULT, cease all communications and contact with him, and work on saving your marriage in order for anything to turn around. Even then, it may STILL be hard for you to trust her ever again. Once broken, it takes time, healing, work and effort to mend the broken trust and to rebuild trust. You will likely feel very mistrustful of her for a while before trust can be regained. But the first step is her taking full responsibility for HER decision and HER actions. In no way are YOU responsible for HER choice to cheat and have an affair, even if you are an a-hole sometimes. The only way to get past is is to get through it. My husband cheated, I never got past it, we did go to counseling, but he didn't help to rebuild the trust. We divorced for many reasons other than his cheating, but in my experience, it's very difficult to overcome.