As someone whose husband cheated ... this is my humble opinion, based on my sitch ... my exh can hold a grudge better than a camel can store water. He literally feeds on resentments, nurtures them like the Cookie Monster collects chocolate chip cookies. This is NOT the recipe for happy and healthy relationships of any kind. It fuels most of his behavior.
I believe he justified his affair because of his anger and his resentments. Did we have problems? Yes. Did I contribute to them. H3ll YES. I don't think anyone can be in a 26 year relationship without some resentment growing on both sides, or mistakes being made on both sides. We are human, after all. But I also know my exh, in some ways far better now than when we were married. He absolutely justifies the most outrageous behavior based on his whim du jour, which also is colored by his anger and his resentments.
As far as LH's point on expectations - I agree, but I also think that some of the expectations people have - in fact, the ones that probably cause the most problems - are the unconscious expectations, whose very nature makes it impossible for them to be clearly communicated.
Again, I see this with perfect clarity in hindsight, certainly, in my own sitch.
