I found out a year ago from him and tried to gently talk to her. She denied everything but was a complete emotional mess and said things that gave her away — it was so sad and clear she was in love with him.
Dave (names changed) has been married for 25 years to an amazing woman, and they've truly had a great marriage in many ways. Mary's been in a couple of long-term relationships but has never married and the man she's with is still living with his ex platonically — she's given up on marrying him. She's got a long history of being "the other woman" or competing with women who aren't completely in the past.
To complicate it all, I was once Dave's girlfriend and introduced them. We had an intense relationship, and I loved him dearly, but he used her and other women to make me jealous, and so I left him for another man. Dave and Mary dated for a month immediately after, and she ended up getting involved with someone else, too. He would tell her I was this great love (he never told me that, BTW). I'm thinking that had something to do with the brevity of their dating. Instant karma! Dave clearly likes women to compete for him. So to kill the game, I simply stopped contact with him for years until he and I were both married because we have a great deal in common, but still rarely wrote. But then the confessions began.
When Dave met his now-wife and was about to propose, he told me he hoped Mary would realize she was going to lose him and say, "No, you need to marry me," but she didn't. And he's mad at her for that. To this day.
When he confessed this and more, I asked him how he and his wife could possibly socialize with Mary, given his strong feelings for her. He says it's because he can control himself. I'm sure too it gives him some sly pleasure. And as if that all weren't enough, he also hit on me as well, calling me "his soul mate — my wife certainly is not" (if it were my vote, I knew she was, really). How his great love for Mary fits into all that ("I lust after you equally, but Mary has the edge romantically"), I have no idea. What insanity. I realized he wasn't just once-an-immature-but-otherwise-cool young man — he was a pretty horribly manipulative guy.
So I stopped contact with him again. That was a year ago.
I have a question for you: if it were you, would you, as the wife, want to know about this? I would. But I also don't want to be part of this. So I keep on going back and forth. I'd like to do something. Ugh. Maybe make an effigy of him and burn it? Thanks, everyone!