I knew intellectually when I caught my ex cheating on me about 9 months before it finally sunk in viscerally. She made a few token gestures about trying to "fix" things...maybe went to the marriage counselor with me 4 or 5 times, then stopped going. We had 2 young boys, so I walked around in disbelief for half of that interim time. Then one night I saw a scene in a movie that was just like a gut punch to me, that kind of encapsulated the coldness and tragedy of the whole thing, and I hit catharsis - - cried my guts out in the house by myself. After that I was cured of her - - there was no going back.