Why can this guy talk to other girls and not me?

This guy that I like at my school always stares at me but NEVER TALKS to me. When I catch him staring, he’ll try to hold eye contact with me (he stares from across the room). When he’s with his friends & I come in the room, they’ll all stop talking and stare at me. I even notice that he’ll step away from his friends & stare. Whenever I walk by him, he’ll turn his whole body around & stare at me. Also, when we’re walking by each other from opposite sides, he’ll either look at me then look away, or he’ll look at me and smile. He even stares at me when I’m talking to other guys. I go to our school football games (he’s on the football team) and I see him staring at me on the sidelines and between plays. My friends always tell me he’s staring. He knows I like him, but sometimes I don’t show it. I have no idea why he stares so much. One thing that concerns me is that he talks to all these other girls (not in front of me) & he flirts with them, but he can’t talk to me! I worked beside him before & he never talked to me, he’ll tease me when we’re with another co-worker but alone he’s quiet. Why can he talk with others girls & not me?