I suppose there are various reasons you need all the details...
1) So that you dont get side swiped emotionally in the future when a left out detail comes up like it just did.
2) So that you can try to figure out what was going on in his brain to have caused him to stray.
3) As a means of him proving to you his honesty and openess.
I agree with my birth brother - if I betrayed and hurt someone as much as your H did, I would be moving mountains to make you happy. I would not be bringing up some trip you did to New York to meet up with a friend who was going through a similar marriage trauma.
