Then this is not about the monogamous secondary being satisfied. He sounds satisfied enough for now with your arrangements.
It is YOU who is not satisfied.
I've just given him a choice, or as he sees it, an ultimatum. I either want a shot at being a lasting partner, which means he stops shopping around while we experiment with how much we can give to each other, or I want to know it will never happen, and I will take a couple of emotional steps back.
So... you've already done all you can. You have owned the responsibility and stated your wants, needs and limits. Now he's got to have time to process that and get back you on that one. Where are his wants, needs, and limits. And see if there's a natural line up, a negotiated line up, or best to part ways.
I don't see where you can be doing anything different here. You are in the hang time. And he cannot be rushed in his process time. So... hang. *shrug*