To "grass" friend up about his affairs

[DearDeadrie]

Me and my DH have been friends with another couple for over 30 years, they met through us and are married.
Due to them being mutual friends my DH speaks to him and i speak to her they have both had affairs but only my friend was caught out, she suspected him but he convinced her he was faithful even though he wasnt.
I believe he had the first affair but not sure as we don't get involved.
The last affair (hers) was outed 18 years ago and as far as we know they worked things out.
Every now and again during social events he brings up her affair and her affair partner and it makes everyone uncomfortable, i have mentioned this to him in private and told him that i know about his affairs so i cant understand why he is with her if he still cant let go of this after 18 years.
Its getting to the point now where my DH is going to say to him either he shuts up or he is going to tell his wife everything he knows about him.
DH is not fussed about losing his friendship but the are part of our social circle so we will still be going to the same events as them.
I hate confrontation and it took a lot to have a chat with him but it had no effect.

No. Ultimatums never get the desired response and unnecessarily up the ante
Why get involved in someone else drama. You presume his wife doesn’t know…what if she does but doesn’t openly discuss it with you?
Don't be a pair or interfering busybodies

if yiu don’t like his company or the content of his conversation simply distance yourself or cash e the topic, he’ll maybe get the hint

hes not going to change his behaviour or uncomfortable digs about his wife affair because you do not like it, he is doing this to elicit a response. He’s succeeding

Typo, if you don’t like his company or the content of his conversation simply distance yourself or change the topic, he’ll maybe get the hint

I wouldn't threaten him with telling but I think I'd point out to him on the quiet that he's being a bit of a dick by still bringing it up when he did exactly the same.