How do you deal or break it off with a guy who isn't even yours?

i know its paradoxical, but i've been seeing this guy on weekends. we've never had a date but steamy make out sessions and take out and stuff. and, i thought he was everything but he doesnt talk to me unless he is getting something out of it, and i can't deal with it. he also flirts with every kind of girl and he knows it bothers me. how do i leave? because when ever i confront him, he says all the right things and he says how much he likes me and how beautiful i am. and i am so dumb for falling, right? so i need help. what should i do? how do you deal or break it off with someone who you are unofficially dating? what should i do?