From reading everything, I am not in favor of telling the OM wife what happened. She might not need the extra stress if she is ill. Of course, on the other hand, she has a right to know.
How many times have you talked to the OM? How was his attitude towards you when he then knew you knew?
I would not believe anything he tells you actually, why should he be honest with you and if he is, he will still minimize the truths to cover his butt.
You might want to actually find out more about this guys wife, from what I read, you are only going by what the OM told your wife. This OM could have told your wife this to get sympathy.
Your wife should be on the look out for a better job if possible, but remember, her changing jobs does not mean an affair ends.
I also think you are doing too many what-ifs in your mind, you are playing mind games with yourself and that can really wear a person out.
Try writing to yourself everything. And if appropriate, let your wife read what you write. Writing is great therapy and can help you think of things you never thought of before.
What is important to you know is knowing the entire truth. Why you wife felt she needed to do this in the first place, which will help to make sure it never happens again.