Have you ever told someone that their partner is having an affair?

[Theos]

And how did I it end up.
( me once could have done. Didn’t. Glad I didn’t tbh.)

idle speculation

No. I would only tell someone I knew pretty well. I wouldn’t necessarily want to know if it was me. People close to me know my views; those who aren’t should mind their own business. I’d be furious at the do-gooder who in many cases is telling for her own benefit ie “good girl cookies”. Hence the saying about shooting the messenger.

I told the person who was having the affair as they were the closer of the two to me. I suggested I had been placed in a awful position and didn't want to be the one to tell his wife.

He took a week away and made the decision to tell her. They sadly divorced but he married the OW and they've had nearly 20 happy years together now and his ex wife is well settled although has never met anyone else.

It's horrible being in such a position as it comes from nowhere and once you start acting on it there's no way back.

I was told a month or so ago that my "D"H was having an affair with the wife of the man messaging me. He admitted it.
I'm still not sure how glad I am to have been told.

Yes. My closest friend. She never spoke to me again

Once yes and she was grateful. I had to tell her he had fathered a child with the OW too. She forgave him and we are still on speaking terms but it was not a nice conversation.

I haven’t but I would

what they do with that information is up to them, but if it were a friend, I’d be more of a shit friend for keeping it secret.

Yes once. My best friend, her fiancée was cheating, and it was so hard telling her. It damaged our friendship for a while but that recovered. She thanked me many years later as the revelation had sent them to therapy, and eventually progressed their relationship which had been stalled for years. They've been happily married for 20 odd years now with no further indiscretions