the reality is that when a lot of people claim that they want an open relationship with their partner what they really mean is they want to keep their options open but don't really want the partner to see others. It's quite common. He is not willing to commit to exclusivity with you but you're expected to. I think you are beginning to see his true colors but I have to ask, if you are into committed, monogamous relationships, why didn't you walk away at the point he even mentioned that he wanted to see others? That's really not an important question just one out of curiosity but the real problem is not whether or not you both see other people but that his expectations are skewed toward him having that flexibility but not you. That won't work out going forward, I don't think. he either gives up on seeing others or you walk away because his true feeligns are that he wants you to only see him.

Oh and added problem in my view is that he wants to date others but as you mentioned only wants to sleep with you. what are you his sex toy now? Sorry to be blunt but that's the impression I get.