How to get over a guy I keep telling myself that I'm already over?

I was dating this guy for 4 months, it was nothing huge at all, we broke up a couple weeks ago because he was flirting with this girl, but we got back together. Then the same week we broke up again because i heard he was flirting with another girl. it was a lie so we got back together. everything was fine from then on until yesterday, i just randomly decided i didnt wanna date him anyway. i mean, hes 14 and he cried a lot and was developed immaturely. So i broke up with him and he was sad and idk how hes feeling now but i heard he was looking at two girls' asses today and walked by them to "get close to them" (boys,.. psh) and SOMEHOW it hurt me, idk why i still care, i dont wanna date him anymore. Please give me some tips so i wont give a **** about him anymore? Thanks!!! :)