Why Would A Guy Like A Girl But Choose To Ignore Her?

There’s a guy at university who likes me (although I’m not sure if it’s because of my looks or my personality or both). But at the beginning of university, I noticed he was trying to get closer to me and I encouraged it. But then suddenly, he went cold. He would ignore me on Facebook and make sure to sit far away from me in seminars (he still does it now).
I realise he is trying to get over me so I asked my cousin why she thinks he changed so suddenly and she said in life things like these happen all the time and I have to just accept it without knowing the reason. Most of the time, he ignores me and stuff but it’s like when I maybe get close to him that he gets all weird with his body langauge. Like today when I was walking out the class behind him and you could tell he got all self-conscious which I guess it cute.
But I simply ignore him now as he ignores me because I don’t want to look desperate (I’ve already tried in the past and he didn’t take the bait). Plus, I only have till May then I don’t see him again for about five months so when we get back, things should be alright. What do you think?
P.S: I know you might think I’m being vain but I’m not. I can tell he likes me because of how he used to stare at me (even though he doesn’t now because like I say, he is trying to get over me).