I really love the advice you all give each other. I'm in heaven.
For what it's worth, this doesn't sound like an ultimatum to me.
if he was seeking "a monogomous life partner which by definition would preclude our relationship," then I could not see him while he dated for that purpose. I stated that if he was seeking to "add a partner to our poly relationship" that I was a-ok and he would have my full support.
It does sound like a way of saying, "I felt hurt when you cancelled our date because I was looking forward to seeing you and I am scared that you might not want to be with me because I can't offer an exclusive relationship..."