I apologized to my XAH for my contribution to our marital problems a couple of years after we had divorced. It was genuine -- I did it because it felt like the right thing to do.
I remember him looking really stunned. All he said was, "Oh I don't blame you for anything." And then the conversation turned to something else. I think he was surprised because he had cheated and left me with our 3 daughters. He still lives with a lot of shame, I think. Sort of sad, really, because I carry no resentment or anger. I forgave him a long time ago, which he also knows. He just hasn't forgiven himself.