Why would a guy act like this?

This guy had this huge crush on me. We’re 16 (year 11). He used to show all the signs (staring, glancing, copying, imitating, stands closer etc.) and I showed signs back.He shows few signs now. We used to flirt with each other all the time but now things are different kinda. We never talked to each other so I decided to say Hi but he didn’t seem to care and didn’t seem interested in the conversation. I just wanted to be friends with him ( I thought this way we’ll be more friendly rather than fancying each other) He is confident and not nervous (he is NOT shy). He talks to everyone except for me he talks and flirts with other girls.He laughs and jokes around with them. I even told one of my friends who I trust. she said some boys are like that but I know that he never used to be like that. I know I shouldn’t care much. And he isn’t exactly shy and he talks to everyone but me. He has never said Hi to me and when I did say Hi to him he wasn’t interested. He talks to girls in front of me. He even copied the things that I do. (he did that for ages). But I don’t see whats wrong with him. I mean I talk to toher guys but I don’t make him jealous. He talks to girls more than I talk to guys so I think there must another reason. I think he still does have some feelings for me. Or should I just not care and just move on.. shall I make him try to talk to me ? if yeh then how? Why does he do this? What shall I do? please explain I need help. Thanks.