Why does he act this way around me, and why won't he aswer me on facebook chat?

[LOLthisfun]

Basically i like a guy i have a huge crush on him bigger than my past crushes. I met him in class he is a freshmen i am a sophomore but that really doesn't matter to me, although it did at first lol. So when i first met him i walked into class late we looked at each others eyes and i think that we fell for each other at first sight (i know it is just attraction), any ways since then he has tried to get my attention although i am not sure if it is to get my attention or if he is just being himself(he is the class clown type, but smart). We sit by each other,he moved to sit by me by the way but then someone was put between us and now we are a person apart. He has tried to talk to me. Like one time he asked about what was going to be on a test and i really couldn't get myself to talk so i just mumbled and pointed to vocab. and stuff. Then he started to be a little closer like moving from 5 tables away to just 1 table away at lunch and once he got up when i was going to through my lunch away, and another time i think he was going to walk me to class but chickened out like he just looked at me and i looked at him we were like 2 ft away and i don't know why but i got too nervous and just went to my friends. Then we got partnered for a experiment with someone else. When he heard that i was going to be with him he got exited, and started saying how cool and stuff but talked more to the other person than me. We went out in the halls and he just walked like at sometimes he walked slower and them at other times he walked faster, he said my name every time and was really sweet after we were done he said good job it was really cool plus i thought that maybe he didn't know my name but turns out he did and the other day we were doing another experiment and he was like what is that girls name she sits by me but he didn't know her name. So I sent him a fb friend request and he accepted like in 4 hours. At first I thought well I sent the fb friend request so he should say hi on chat first. Every time we were both on chat is he goes offline. Then once i gathered the courage to say hi thinking well maybe he is as nervous as me but then he didn't say hi and just went offline like immediately. I got really mad and the next day at class i didn't even look at him nor laughed at his jokes, he seemed to stop making jokes that day in class b/c and he seemed kinda sad so i felt bad and a week later i said hi again waited like an hour for him to reply all through this he was on chat but never responded then i asked him about a project like what he was going to do, no replay at all but he was still on chat after waiting like another hour i decided to go offline well i checked 12 min later and he was offline. Can someone tell me what is going through his head. Plus i think the teacher has cached on that we like each other b/c he asked him like what was going on in front of me and said
Teacher: "Hey whats going on, u been a little late on H.W."
Him: "noting just after school activities getting in the way and kinda busy thinking about...stuff" " Teacher: Who is she"
Him: " nervous laugh... no one"
Teacher: "Tell me about her after class? Any seniors asked u to prom"
Him: "One did but i said no b/c i wasn't interested" all through this i was looking down at my desk blushing.
PS: I love that teacher he is cool.
He just wrote on his status that he was waiting in line for 2 1/2 hours to get an autograph from some football player of his favorite team could this explain why he didn't answer and next time should i once again say hi?