Why does my friends with benefits treat me like a girlfriend or something?

k so my friends with benefits and I act like a couple. We go to each others houses, watch movies, meet each others families (well I only met his family 5x, he hasn't met mine's yet) he comes to see me and spend time with me on his break from work. We have quickie sex but then the rest of the night, we're up talking and cuddling. He gets sorta jealous if he sees me texting a guy friend, saying oh you texting a hot guy, I see how it is. When he's texting or talking to some girl, I get jealous too. I don't want anyone taking him away since I'm kind of possessive, and I really enjoy the sex but I don't think I want a relationship yet. Neither does he. But it's confusing when he says he doesn't want to have sex all the time, he just wants to talk, hang out, and cuddle and kiss me. I love having sex with him though so every minute I get, I would screw him. But I feel like I'm sort of in some kind of relationship because we talk almost everyday. I miss him when I don't see him once a week and when I do, I always give him a big hug and a kiss. Or he'll sneak some kisses when we're alone and says sorry about that he just couldn't help it. We hold hands and do a lot of lovey dovey stuff where I feel as though maybe this could turn into a relationship, but I know it won't. But why does he do these things if all he wants is an fwb?
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oh yeah and when I ask him about the girls, he'll say their alright or so-so but not hot like me.
Why does my friends with benefits treat me like a girlfriend or something?
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