He says this would be best, since my hooking up triggers him. But they were cuckold couples, GMHC, and the half who didn't "get to" hook up with others didn't want to hook up with others.
The cuck half of a cuckold couple gets off on their partner "cheating" on them.
I agreed to a monogamous relationship, and I've gone a year without hooking up with anyone else.
He seemed genuinely relieved and said he felt more secure.
So with your couples therapist there to mediate, tell him your marriage is either open or closed.