I have not read anywhere on what to do if anything about OM. Do I just ignore this or do I confront him in an adult manner?
Thanks
Him? No. Don't talk to him at all; you confirm in your wife's eyes that he is a worthy replacement to you if you feel threatened.
His wife (if he has one)? Absolutely. She has as much right to know what is going on in her marriage as you do in yours.
As for what to do about the affair? Assuming you have proof (emails, letters, pictures, whatever), confront her about it. (Do not give up your proof -- all she needs to know is that you have it.)
Tell her that you do not intend to live in an open marriage, and give her two choices: end the affair, or go move in with him.
Me: 44, Wife: 39 M: 17 years T: 20 years Bomb on 08/25/09 1/13/10: MC started 1/28/10, 2/8/10: More bombs 8/28/10: Wife moved out No talk of D, no movement