How can I avoid being treated like crap by men?

Stop going for the guys you think you're attracted to, obviously you're going for the wrong guys, try dating outside your preference. And stop having sex with them, YES if they ask for it and you say no and they leave you, then they're no good. You sound like a great woman, hold your head up and hang in there you're 21 you've got plenty of time focus on your life and eventually he'll come around :)