So the consequence for continued contact with OM should be she moves out of the house or I move out and go dark? Do we still go to MC if either one of us moves out or I go dark?
I think the others here have answered the first part, so I'll give you my take on the MCing.
I would let her know that "I have no intention of spending our family's finances on marriage counseling while you're having an affair." You could either tell her this directly, or you could say it in front of the MC, and try to get the MC's agreement (most do agree that MCing can only be done without a third person involved).
