I need some advice about a situation, I'm going to keep it slightly vague on the odd chance that someone involved reads this (unlikely I know) but basically I had a 'situation' recently with a man I subsequently found out was married. Actually he told me he was separated and I believed him until I came across some information which led to me finding out. We never actually had sex but he definitely would have and during the time I knew him (I've since stopped contact) he told me about a few other encounters he'd had. I'd met him on a website that was basically geared towards sex I'm embarrassed to say, so this wasn't such an odd thing for him to tell me.
This was a little while ago but I can't shake off the question of whether I should tell his wife. I've found her on Facebook (which feels intrusive in itself) and could send a message but then I would lose my anonymity so I'm anxious about doing that.
On the one hand I feel she has a right to know he deliberately went looking for sex over an extended period of time. On the other hand I hate the thought of ruining someone's happiness, and they have children too who would be affected.
There's no connection between us so I'm not worried about it having consequences for me (obviously I genuinely had no idea but wouldn't want what happened to become common knowledge).
He's still at it, too (I won't say how I know).
Please advise me on what to do.