I did confront OM, but the A was already over by the time I found out about it so the situation was different. There are many threads I have read on the boards where OM was confronted, including one where the OM was the LBS' cousin! So much for family.
There are 3 outcomes, 1 OM won't talk to you, 2 OM gets belligerent, 3 OM is apologetic, tells you it will end, then keeps it going (lies to you).
Grace is 100% right that it will drive W farther away and OM will move closer.
Do you know OM?
When I was considering confronting I spoke to DB coach. She actually told me to do it if I needed to. She said that some men will respect that, and I he's looking for a reason to get out he may take it. I that happens though it is on you. You just took happiness from your W and she WILL resent you for it.
That said, it's your decision to make, just think it through. What do you want out of it? How can it go wrong? What will you do if / when it goes wrong? Is the potential cost worth it? You decide.
Accuray
Married 18, Together 20, Now Divorced M: 48, W: 50, D: 18, S: 16, D: 12 Bomb Dropped (EA, D): 7/13/11 Start Reconcile: 8/15/11 Bomb Dropped (EA, D): 5/1/2014 (Divorced) In a New Relationship: 3/2015