Why Does He Treat Me This Way ?

I know this guy from the olympic pool we use to talk on facebook about personal stuff he know i'm single & has told me he's single too, he'd compliment me & everything. The at the olympic.p when I catch him staring at me he smiles, he was so nice to me makes me laugh & he's always the one that starts the conversation, riding the bus with me paying being a gentleman. then once a girl kept insisting on him until he started talking to her & TOUCHING (he never does that with me) her though he tried to get away from her, & now he doesn't come to me he just say hi & waves & when I look at him he turn around & go back to his work he talks to my friends but not me, he's different with me but in a mean way, & now he ignores me. & when he knows i'm behind him he never turns around and sometimes look from the corner of his eye, anyway we used to come back from training together & after I started going out with a guy ( one of his friends) he didn't ride the same bus with me.