I do know how to contact him though ... I could tell him myself. I've never met the OM, and I had no intentions of making contact, but I do have his info. maybe it'd be better coming from my wife, to provide more affirmation that it's over (hopefully).

I'm glad I'm choosing to share here before I do anything :) thanks all..

If you ask her to do it how will you know she did unless you're standing right there for the conversation? How will you know the CS will tell his wife? Arrgh! He can just sweep it under the carpet.

I was thinking I could watch my CS to write & send him an e-mail, or text.

You're right though, what he does with the information is out of my control. But maybe it'll help him come clean, if he has the notion that I might try to contact his wife.

I suppose your wife could give her former AP notice that you plan to message his wife about the affair on some particular date. That would probably push him to tell his wife first. Depending on what you heard next, you could actually message her if needed (find out his and her names and locate her online).

The thing is, you have no idea what dynamic the other relationship has. Maybe she's madly in love and it would break her heart, and you would be the catalyst for her hopes and dreams to come crashing down even though you are not at fault. What if he is planning to tell her and they end up working it out because he decides to be honest. Or things may have been circling down the shitter for some time, and you'd giver her a reason to leave with no remorse, freeing her from a toxic relationship.
You need to self reflect and decide whether or not you really feel sorry for her, or people like you and her, or if you just want to act out and hurt someone/anyone at the moment, because it will definitely affect all 4 of you. That may also be a motive for you, because it gives you a sense of control over a terrible situation that you were thrown into.
You're not friends with either of them, so you have the least to lose. However, if I were you, I would stay out of grown people's problems. The only obligation you have is to yourself, and to your own relationship. Bottom line, you'd be meddling. So do you want to do it for her, or for you. And if it is for her, will you become an activist for all cheated spouses outing every affair you cross in the future, or is it just this one time, because you are somewhat connected to her?

Honestly, there were people who knew in my situation, and I wish someone would have let me know. Anonymously probably. And I might not have believed them. But I was already questioning it in my mind, so to get that confirmation would have helped.

Every situation is different, that is true. But my response when people ask this is usually to say: to send an anonymous letter, give specific information if you can, and then be done with it. There is no good way to find out, but they need to find out. The cheater already ruined the relationship; you letting them know or not doesn't change what's happened. I think the betrayed spouse always has the right to know.

My husband was in a long-term affair with a co-worker. I know her and her husband. I confronted my spouse, he swore he'd end the affair. He didn't, of course. They just got sneakier. I finally went and told the other woman's husband. Things changed right away. He was so grateful. He knew she was cheating, didn't know with whom, my H was on his short list though. I wish I had told him right away.

I say tell. I am sure you can find out who exactly these people are. You can always ask your spouse! Tell your spouse you are going to tell, too. Enough with the secrets!

I think you should tell him directly via an email from your wife and you, and it could go like this:

'Dear AP, my husband and I are going to reconcile our marriage, and we can no longer have any contact. We are both sending you this email. My husband wants to contact your wife, to tell her about our affair, and will be doing so this (pick a day). We would prefer if you told her, but my husband doesn't think you will, so he's going to allow you until (the chosen day) to tell your wife yourself, before he contacts her directly. So sorry but this is the way it has to play out.'

I appreciate all of your input :) I've learned that the AP may have been separated and still is. So it might not even matter now. I'm going to try and find out if that is true or not and go from there.

Find the wife and tell her. End of story. Use a key-logger to get whatever contact info you need. Arrange to meet with her for coffee to discuss what you know. Make sure he knows about. Turn the tables. This is the worst case scenario for him and he has earned it. Just imagine the pillow talk between the OM and your wife discussing YOU. Now you're getting together with his wife discussing HIM. Time for you to take the driver's seat. Her devastation sucks but is not your problem right now. You've been savagely wounded by this asshole and the person you trusted most in the world. Focus on yourself and your survival. Time for selfishness.

He's left his wife. and yes, I'm still going to find her.