Do I tell the OMs wife

I note their fear of work of work finding out. That's where I'd be focussing my attention- yes there's an argument they might loose their jobs and you / the OM's wife are worse off financially. But if work find out, it's likely to get back to her and you won't be the messenger.
Or at the very least I'd make him sweat that it's a matter of when not if you're telling their employer. I couldn't countenance their smugness and my complicity in it by not saying anything.

If I was the wife I would want to know. I'd hate this going on behind my back.

I’m so so sorry you’re going through this - and I admire your stoicism. I hope you have some support around you.

I can understand your reluctance to say anything, however as it is clearly still ongoing she has a right to know, for two reasons:
1.in case he’s about to leave her she can get herself prepared so he doesn’t blindside her. With a young baby she’s potentially very vulnerable, both in terms of mental health and practically in terms of living situation etc.
2.the risk to her health is clearly ongoing

But only if there’s no risk to you or your children.

However, if you feel you can’t because you don’t have the bandwidth right now - I would absolutely have to make her husband sweat, particularly as you know it’s ongoing. I couldn’t have him ‘thanking me’ - it just makes you completely complicit.

Tell his wife. She should know. For her health especially.

I don't think you should feel under any pressure to tell the wife unless you feel that you're ready and able to do so. Your priority needs to be yourself and your kids.

You may feel empathy for the wife, of course, but ultimately, it is her husband that has a duty towards her - he is the one that made the vows to her, not you.

What I would say, though, is that you should definitely plant the fear in her fuckwit husband's mind that you're going to tell her and that you're simply biding your time. Thanking you for not having told her yet is beyond crass. Let him sweat.

And that's only right @Noideawhat2do.
I am one saying that the wife should know but it's only one thing amongst others. What is important is that you look after yourself and your DCs, that's the priority.
Everything will fall into place in its own time, don't worry.

Shouting at you and harassing you everytime he saw you is very different to what the OP is suggesting doing. That's not just telling the wife.

I do agree that your husband still holds some responsibility for making your life hell, he had the affair and bought this angry man into your life, you were obviously caught in the crossfire of this man's anger towards to husband. If you piss off angry men unfortunately your family will be collateral damage. But you also have every right to hate the OWs husband.

I was the wife. It really hurt that everyone else including a good friend had known. I felt so stupid. Tell her as she deserves to know the truth and then she can make up her mind as to what to do.

We are not going to agree, my sister who was in a terrible place, she’s now free from the cheat, is now in a great place.

What she did, you may say was inappropriate but it wax a reaction to the cheating husband and the other woman. The whole thing pushed her so far.

A result of the cheats cheating.

The OP and the person that he wants to tell have not had the affair. I didn't have the affair yet it was me who was the victim of the husband's need for revenge.

Your sister is in a horrible place... I have been there and got the tee shirt. No one is blaming her. All I have said to the original OP is that if he is telling the wife out of revenge against his own wife and her affair partner it is not a kind thing to do. She may not react in the way he expects and he has too much skin in the game to be doing it solely for her benefit. If anyone else had told me I would have been grateful for the heads up... He just wanted my husband's life to fall apart without any regard for anyone else. Revenge is a very selfish act

Can you tip her off anonymously, so you don't have to deal with the fallout?

Enjoy my evening? What’s that all about? Very PA!

having seen my sister completely change after discovering her “d”hs affair, I’ll judge heavily anyone that says she was wrong.

Enjoy the rest of your weekend.

Sorry, I think your take on this is really strange and you seem to be being deliberately obtuse. Enjoy your evening.

You’re talking bollocks as you’d realise if you gave it a moment’s thought. Nobody is responsible for anyone’s behaviour but their own. You can only be held responsible for things that are within your own control.

He and his wife are still together.
I am not blaming him for the affair... I have been very clear in that. I blame him for telling my friends, neighbours and parents ( he went to their house to lay that gem) about what was happening in my marriage.. It made him feel better. He didn't tell his family or friends...just mine. His rationale was that I hadn't kicked my husband out... So he thought that my husband hadn't had had any consequences for his actions. His need for revenge ran roughshod over me and my children. That is what I can't and won't forgive

The equivalence is that having an affair when married, causes dreadful repercussions.

So, don’t do it!

In my case the OW H tried to me. I wished for years that my h didn't tell me first. Now, I'm glad I knew and I've divorced him over something else. But while we were still together and thought we always would be, I wished I'd not known.

Tell her. I think the husband is a knobhead for texting you to thank you FFS.

He caused it, when you wrong someone and mess with their lives, it has repercussions.

This was a repercussion from his unfaithful wife and her unfaithful husband.

But you felt you could save your marriage, he probably didn’t.

If your husband and his wife weren’t so awful, it would never have happened. I hope they’re both thoroughly ashamed of themselves.

I also hope the OM has moved on and found peace.

He was a victim, you’re victim blaming him.

We are not going to agree, so we will have to leave it here.

I hope your husband manages to not let you and his children down again.

I blame him for his behaviour. No one else's... Just his. I know he was done over by his wife and my husband but that doesn't mean I have to forgive him for his poor behaviour towards me. You can have bad things happen to you and still be a dick. Yes he was driven by revenge and anger. I was too but I didn't drag him into how dealt with it just to make me feel better.

No he wasn’t. He was responsible for having an affair. He most certainly wasn’t responsible for another man bullying and harassing her.

I would never blame my sister for her actions on finding out about her “d”hs affair!

Well no, but you weren't also a wronged party in that affair, presumably? And she's your sister, not some random bloke shouting at you in the street. It's hardly equivalent.

You can be annoyed but you can’t blame him, I would never blame my sister for her actions on finding out about her “d”hs affair!

She thankfully split and is 100 times better now, but those dark days were awful for her.