Just to add my 2p worth, have been there myself, forgave (could never quite get myself to forget) it ate away at me for months, I constantly doubted myself, wondering why I wasn't good enough, let myself get turned into a complete doormat, which he took advantage of and treated me even worse.
Eventually I found out about numerous other affairs, including attempts with my 2 closest friends.
Walking away was hard, I went for a very comfortable life, to living from pay check to pay check, it would have been so much easier to stay, and I did consider staying and just having my own string of affairs to get back at him. It was hard, it hurt like mad, I lost all confidence and self worth.
But looking back 10 years later, I wish I had done it sooner, the baggage of that first time never left me, and even in new relationships I found it incredibly hard to trust anyone. I'm now back to my old self and so happy again.
Sorry to have to say this, but move on. Can you really ever trust her again?