I did the same thing with an angry email. I overreacted and sent a terribly hateful, rejecting email. Within the month, he had moved OW into his apartment.
I think it's great he is trusting you again. I can see how you want to treat this reconnection gently. It must be nice to have his perspective on the OW. Sure doesn't seem like a fabulous relationship and his telling you this truth is so validating.
He seems genuinely sorry for the embarrassment he has caused you at work. Or, at least, he seems to be in a bad state and willing to accept his contribution.
Heather
"You know, it's times like these when I realize what a superhero I am." Tony Stark/Iron Man
“Focus on what you can do, then do it with all your heart.” Lois Wilson