He can't look in my eyes anymore, but we like eachother?

In college me and this guy like eachother I think longer for him but my problem is he could look in my eyes but sometimes he'd look down. Weve never really talked in class and so I started chatting away online with him talking and he asks me questions. But since he has got to know me he can't look in my eyes and if I catch him looking he stares at the floor and he can't look at me unless I talk to him. BUT when we were at a uni open day me him and a couple of my/his friends he did try talking to me but he couldn't look in my eyes while he was talking and he seemed more relaxed than in class. If I ask for help in class he'll puff his chest out and look at me and lower his tone of voice to a softer one and slightly forget what I asked him in the first place. Why can't he look at me? =/