That being said, if my W agreed to MC, I would not say a word about the OM. In my opinion, if she agrees to MC, then the OM is not all that and is fading fast, otherwise, he'd be her world, and MC wouldn't be an option.
Jon,
I think you're discounting the SIGNIFICANT number of wayward spouses who use MC as a false pretense to pretend that they tried. It happens. I actually overheard my wife, during her affair, talking to her brother on the phone, saying "I'll go to the counseling, just to show Mom and Dad and the kids that I tried, but there's no way I'm getting back together with Puppy."