I'm trying to get over him, but he keeps sending me flirty signals? And he has a GIRLFRIEND?!!?

there's this guy named tyler who i've had the biggest crush on at the beginning of this year. he's really shy and the only times he actually talks to me are when he teases me or something like that. He got a girlfriend, and she's not that cute and he only refers to her as "cutie", and they never even hang out!! but anyway he keeps sending these weird signals, while he's going out with her. like he's always checking me out (subtly of course), he'll get up in the middle of the clroom like at least twice a day to blow his nose and he'll turn around to see if I'm looking at him, he acts a little strange if i don't pay any attention to him, he'll get annoyed if i "flirt" with his friend, when he goes to the sink he'll squirt water at me so we get into this "water war", or he'll chunk a pen cap at me for no apparent reason at all. I don't know what to do with him, because I'm not going to into his relationship, and I don't even know if he likes me or not!! PLEASE HELP?