Does he like me and is just shy?

There is this guy in one of my classes. Some days it seems like he really likes me and then some days he acts like he doesn’t even notice me. He does the whole staring at me and then looking away really fast thing. If were waling in the hallway he walks with his head down or he walks really fast. He won’t talk to me. Today I was sitting with one of his friends. Then his other friend came over and sat with us so he was by himself. Finally he came over to us. There was still one chair left in front of me, but he wouldn’t sit in it. He sat off to the side in the other row away from us. If I’m not with his friends he’s always with them and has no hesitation about going up to them. His friends are always whispering about me and staring at me even if I don’t know them. Do you think he likes me? Why is he different on some days?