I am very sorry about the recent development. I know the pain. My heart is going out also to you.
What your H said is not reasons at all. But that is how he tries to justify his A. By blaming the fault at you, he can feel better. Of course nobody is perfect. He might have reasons to feel recentment on you. But having A is not a solution he should have taken. My W has also a similar reasoning. That I did not help enough on house work. When I took over most of the house work for the last 2 years, to show her that I was not fuzzy about house work. But she still continued her A. So it was not the real reason.
I think your H probably has a strong emotional attachment to the ow. That's why he can't let go. If the ow is still married, then it is very complicated. If you informed her H, depending on his reaction, you may speed up their separation. That is what your H wants.
