Well! I must say that you had a day of it. Now, here are my thoughts...definitely tell your h about the conversation...do not leave anything out. Be sure you have his undivided attention when you have this discussion.
As for the ow, I don't trust her one bit. She may have been sincere in some areas, but something tells me that she was testing the waters to see just how much you knew and what you were going to do about your h, i.e, kicking him out and/or divorcing him. In my opinion, she was on a fishing expedition.
You are a saint. You've earned your wings, halo and harp today. I think you did a smashing job of handling this discussion w/her. But, please watch your back.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.