He reckons he is not your boyfriend? If you are staying at his a lot, sleeping together, having a relationship, then I would say it's a fair assumption that you think you are his girlfriend. I think since it means a lot to you, you should tell him that you want to be exclusive. If he doesn't, then what that means is that he is happy to be having sex with other women as well as you. Sorry, but that's just icky! And what man wouldn't like to have lots of women, given half the chance? Be strong and be strict! Tell him what you feel and say that either you are exclusive or you are going to find someone who loves you enough to want to be your boyfriend. I mean, it's not much to ask if it?!