Tar,

I wouldn't go that far. I think it is important to keep MC appointments.

What we all have suggested is to state your no-OM boundary and reinforce your stance that you will not live in an open marriage. What this entails are the following action steps:

1) W will need to end all contact with OM immediately
2) W will need to write NC letter and send to OM after you've read the letter and approved it
3) W will give you access to smartphones, laptops, computers at your request ...including her passwords
4) Restate this to W in front of MC so the MC can be supportive of this process
5) No "happy family" activities while W is still involved with OM

If W balks at or refuses to do ^^ all of these action steps, then I would step away from MC with her and continue with IC for your own benefit

This information isn't new at all...we all have said this in previous posts to you.