The truth is It does not matter what somebody did to you. You should forgive them. This doesn't mean that you have to stay with them, that decision is yours only to make. But as far as forgiveness is concerned, there is no limit. You don't run out of forgiveness. When we forgive others we set ourselves free from the bondage of that pain and of the revenge that comes with it. Forgiveness does not run out. I don't care what anybody says. Everything deserves forgiveness even murder.
He has shown you who he is--believe him. When a man cheats on you and you take him back, you will be sleeping with whoever he slept with--remember STDs? Dump him, get yourself tested and get on with your life.