Why is this guy ruining my life?

me and my ex broke up last february, we had been on and off for a while but we were in love everyone knew it. since we had been on and off so much i didnt think this break up would be any different until now im sitting here almost a year later still without him. we didnt speak for basically the rest of the school year and go back in touch over the summer we started hooking up and i didnt wanna get my hopes up but was pretty confendent we were going to end up back toegether but he would be very weird with me only talk to me like once and week and if he knew there was a party he would make sure i was going i felt like he was using me but i wanted him so bad i just let it go. once the school year started it was the same old noting was getting done it was almost like i was just that girl until he found something better. and today i over heard his 2 best friends talking about some freshman that he messaged on facebook it made me really upset because we hook up on the weekends and when i got home i went on his facebook account and i found all there messages to this girl whos 2 years younger its was very obvious hes trying to get something out of her and now i just dont know what to do im so upset and so angry with him i love him dearly but i dont think i deserve this why was he brought back into my life if it wasnt for the better i dont need 2 heartaches. not to be conceited or anything but im very pretty and could get someone better but im just not interested