Why does this happen?

I know there are hundreds of ques like these..but I'm really lost...I like this guy who's 20, only 2 yrs older than me..I just thought he was saw nice and loving..he used to always ask about how I am and how I'm doing in school..but now all of a sudden it's like he's deliberately avoiding me...I mean he still says hi..but that's about it...very brief..idk why he's doing this..i mean I realize that he'll never like me back..but why can't we just be friends...cuz he's normal around other girls..