Need to ask about the "Fog" of people in affairs

[Michael Mc C]

Is it o.k. to contact OM and let him know I am aware, I'd like him to end it somehow, or I'll let his wife know?

I would not say that it is "okay" to make contact as a general rule - it is something that you would need to decide on AND understand the possible consequences for doing it. I contacted W's OM on the same day that I confronted her with the proof. She was aware of what I was doing as well.

Things were already very ugly that day. I didn't care how she reacted at that point - as far as I was concerned I wanted her out of my house. Things did not continue down that path, thankfully.

Contacting the OP can be the worst thing you do as it could drive the wedge between you and your spouse deeper in my opinion. If the OM doesn't care one way or the other, or if he's not aware that your W is married, contact MAY dissuade him but I wouldn't count on it. Just know that it is may be thought of as controlling.

And if OM is married he may just not care if his W knows.

I'm sorry I'm not really answering your question. In the end you need to decide on your own based on what risks you're willing to take.