Feeling tricked and used! PLEASE HELP!!!!?

so there was this party and this guy i like was there. we both ended up sleeping over where the party was because we stayed after to help clean up. so we had to sleep together on the couch putting two together & one blanket. well we layed down and it all happened so fast! hee started kissing me all over my body and he took my shirt and bra off and he unoned my pants and fingered me and i was jacking him off. it was an awesome night. BUT he used me! he has a girlfriend! he wants to be with her and not me after everything! i was so bummed! im not an easy girl but i REALLY REALLY LIKE HIM and ive known him for a long time now. and im so confused! i feel really bad and empty and so many other feelings! what should i do?????? after what we did made me like him more! please give me your best advice! please.