I really dnt know what to do..?

Okay so theres this guy.. His names is Oscar i like him & all & he likes me we actually kissed a couple of times but then one day he told me he has a GF theyve been going for a year & something months i was shocked :O i felt bad cause i felt like he was cheating on his GF wd me ! & now he tricks me into kissing him & stuff but then when i go on aim hes away is like iLoveyou babe & all of this what do i do ! BTW he goes to school wd me & his GF dnt.. I js dnt know what to do i also told him this has to stop now but he always gets mad at me wtff do i do ?! HELPPP ! :[