How about something like "I understand you don't want to end your friendship with OM; thank you for being honest with me. I, however, cannot live in an open marriage where my wife puts her friendship -- assuming I believe you, and we both know you're lying to me right now -- ahead of her marriage. I guess I have some thinking to do."
I don't like the lead -- it accepts her premise. Which, let's face it, this morning's contact with OM pretty much disputes.
You could either do it now, or you could make a stand in front of the MC, if you think they would be supportive. Something along the lines of "Look, I'm more than willing to face up to my own contributions to the problems in our marriage. But I'm not going to waste my time, nor my family's finances, nor will I disrespect YOU, (MC), by not being completely honest with each other in these sessions. (then turn to wife) (Wife), thank you for being honest with me, at least, about the contact with OM itself. I, however, cannot live in an open marriage where my wife puts her friendship -- assuming I believe you, and we both pretty much know you're lying to me right now -- ahead of her marriage. Now we can either put this thing right out on the table, in all its glory, and call it what it is -- an emotional affair, at least -- and try to DEAL with it, or I guess I have some thinking to do. Because this is just a sham to ignore it."
