Why does this guy act like this?

I have liked this guy for a while, and we are both 17. We met last year, and became friends but he did not like me. I lost around 60 pounds over the summer, and he started making a lot of ual jokes to me. He would suck on his pencil when I looked at him in cl, to refer to me giving bjs, mentioned that I should join him in his (which wasnt going to happen), and he became a lot more interested with me when I would not know a ual reference and liked explaing it too me.. I am a virgin, I have never had a bf but have opportunities to have but I am not a . He also would tell me I was his partner in cl, and not ask. And when I was upset or had a secret he woyld bug me and call until I told. Why is he behaving like this and treat me this way suddenly? We were friends..