Thats a sticky situation. Now that he knows you know, he may tell her himself. I would have to go with Michael and BobbiJo, if you decide to be the one to tell his wife, you have to be prepared to deal with the aftermath, and it will probably be ugly. My H is having an EA/PA and has been gone for 2 months. I have had a couple of texts from the OW, who lives with her parents and I have been tempted to call and tell them, but it wouldn't change anything or fix anything, so I have decided to just let it be for the time being.
Do you want to work things out with her, or are you ready to move on?
M:39 H:39 K:S14;D8 T:22yr M:15yrs S:12/28/07 EA/PA 3/14/08 OW preg 11/17/08 born 12/12/08 his ~~~~~~~ Never allow someone to be your priority while allowing yourself to be their option