I'm a strong believer in karma. It's not just some eastern mysticism as I use to believe. What goes around does come around in it's own time. It's a law of nature as far as I'm concerned. Possibly God's way of teaching us how to treat each other and grow spiritually. I know I've been stung by it in my life time. I've also been rewarded by it. I've learned some valuable lessons.
Let nature take it's course. Nobody can really stomach living a lie over a long period of time. It eats at them. This is not one of those little white lies either, it's one they know has potential to hurt others. Can you live a lie like that without the guilt and regret? I can't.
There is also the possibility that the OW's h may already suspect something? I know I suspected the A long before I confirmed it. Give him some credit, he may already know or at least suspect. Granted, us Men may not have the natural intuition like a Woman, but we're no dummies either. The clues of an affair are two strong to deny even from the most aloof cheaters.
It will only offer you temporary relief and the outcome is impossible to predict. Your choice and it's a gamble no matter how you look at it.
I say let them stew in their own deceit for a while. Watch the transformation as the depression, and low self-esteem starts to take it's toll on him. He'll start to lash out in anger at you for his own issues, so be prepared. Go dark and ignore him.
"It is curious that physical courage should be so common in the world and moral courage so rare." -Mark Twain