Yeah, cause it just sucks.
But it does get better with time, especially if he is remorseful. I sometimes repeat "then/now, then/now" in my head. But there is really no way through the pain but just to go through it.
My fWH says that he feels like a different person now, and he certainly acts like one. So...since I want to be with this man in front of me I try to concentrate on now.
Doesn't always work. But it gets easier and easier.
Best of luck and hugs to you.