How do i get over my ex-boyfriend?

me and my ex had a stupid little relationship, and i broke up with him about a month in. its been about two months and for some weird reason i still get upset when i see him flirting with other girls! i get mad at myself for being mad because he is the biggest jerk in the world! why would i want that!?! but he took the breakup so easy and he acted like he just didn't care and he hasn't talked to me since. i kept telling myself that i was only upset because i wanted him to want me back, but inside i really knew he really didn't care. i feel like i still want the person i THOUGHT he was, but he will never be the way i wanted him to be. how do i get over this? :(