Why is he so mean to me :( ?

there's this guy who said he like me once but i was taking it slow, but was always his friend. before i knew it, i heard he had a girlfriend and now he seems so smitten. now this hurt because i realised i liked him but i accepted it was too late and my own fault really. but what gets me down is that he's so mean to me now. i've always been lovely to him, just because i didn't jump straight in there with him like his other girls probably do. on the facts about your friends application on facebook, i worked out that it was him who'd answered no to the question 'do you think she's a good kisser.' i just felt really upset. other times he's been really cold or rude with me, that's if he doesn't just ignore me altogether. we only really see each other at parties and social events because of some mutual friends so i just want to be his friend. why does he have to treat me this way? :(