what's this feeling? i'm going crazy over it!please help me!

I KNOW IT4S A BIT LONG BUT PLEASE READ IT ALL I4M DESPERATE
i've got this professor who used to look at me alot when he was explaining,always asks me to do presentations even when i don't volounteer,who always smiles when speaking to me,who give me a bit weird looks when even we meet in the hallways.....he kept doing this for like 10 weeks but 3weeks ago he started to totally ignore me now he looks back at me again,smiles.... always corrects the stuff i ask him to correct(he usually forget to correct the stuff students give him but never forgets mine) and i'm not a bad student just like i'm not an amazing one. i mean i dnt talk much unless i think what i wanna say's really interesting. i really think he had a crush on me but i'm not sure.what do u think?(of cours i'm not planning or doing anything i wouldn't wanna ruin the guy's life so please just answer and tell me what u think).
and now the main thing i wanna ask about is that every week i convince myself that he's nobody,that i really don't care about him....(btw i never think of him in a phisical way even though we have so much in common annd he knows that cuz he always asks me for my opinion when we discuss subjects in class...) when i see him i'm totally professional i don't think i show any signs of anything+when i see him it feels like i'm empty on the inside,i just have no feeling at that moment but after the course is done i just can't get him out of my mind(like i said i don't think about him in a dirty way but he's just always there) and i really hate that cuz i don't even know why i feel this way can somebody please tell me what it is AND what to do....?(btw i've never had a boyfriend and don't wanna have one so jst in case that's ur suggestion...)
PS:sorry fr the spelling mistakes i'm just in no mood to care bout them now