Is your counselor solution oriented and pro-marriage?
Marriage counseling is ineffective for couples where one of the spouses has decided to start the process of leaving the marriage and start looking for new partners (she has already been caught forming some sort of relationship with another man).
What does marriage counseling convey as a message in this situation? One spouse wants the marriage to work, the other does not, even if the spouse with the foot out the door comes to counseling, it's really just to put on a show, even to satisfy their ego "well I did go to counseling, he can't say I didn't try that much", etc.
You know the answer as much as anyone else around here, it's to let them go. If they really want out, if they're really willing to let you go and find someone else, the only thing you can do is let them go and move on. Hanging on, going to MC, etc. It's all a form of pursuit.