Sounds like you want totally different things from a relationship. obviously casual sex is his main hobby and past time.
makes me wonder why you both wanted a relationship with each other in the first tbh. Talk to him about it. ask him what makes you special to him that he wants a relationship rather than just sex with you like all the other guys. If you don't get an answer that gels with what you want from the relationship, maybe it's time to reevaluate it.
Just from what you said, it sounds like your want an emotional connection and he just wants someone to hang out with. It's only a thought, but is it possible he likes the idea of being in relationship because it makes his hook-ups seem more "naughty" and dangerous? If he was single and hooking up with guys, he's just another single guy, but if he's in a relationship it could be mentally increasing his currency with these randos because he's already "got". just a thought.