What is he doing to me?

So there’s this guy I’ve known for a couple years but we’ve only ever been just friends because he was dating someone else. Well they just broke up and out of no where he is all over me. I never got any signals from him before and I turned him down because I figured he was trying to rebound with me but now I’m confused and can’t stop thinking about this. The first time he came on to me we had been drinking at a party and he tried to get me to go to bed with him. He kissed me and I kissed him back for a second before I turned him down and pushed him away. I thought he was drunk but later I found out he was drinking water most of the night. We didn’t see each other again until this last weekend but we did communicate over social media (like nothing ever happened.) He told our mutual best friend that he really liked me and has had a huge crush on me since he met me years ago. I was in complete shock because to be honest I feel like he’s out of my league. He’s gorgeous and has girls throwing themselves at him all the time. And I’m not unattractive but I’m heavy and I just don’t understand what he sees in me. And then this past weekend he had a party at his house and he asked me “to be his girlfriend” I laughed it off but he kept cornering me and telling me how much he liked me and why he liked me and that he thinks we’d be amazing together. I kept telling him no and trying to laugh it off (he has a reputation for being sort of a slut) but he was so serious. When I told our mutual friend all of this she said he’s not normally like that with girls and that maybe I should give him a chance. But then later that night we’re at the bar and he’s barely talking to me and there are girls all around talking to him and later that night and the next day he acted like nothing happened again. He stared at me and smiled at me a lot when he was driving me home but we didn’t talk about it. I sound so childish but this is so weird and exciting. So basically what I want to know is do I believe what he’s saying when he’s drunk or do I just ignore it and let it pass for him just trying to get laid?