How to get over an ex?

Ughhhhh i hate myself, I broke up with this guy and idk why. We were best friends for a long time and dated. A long time too. But then he texts me one day and says we should breakup, I was kinda ok with it since I was so depressed I didn’t care abut anything. This happens a year ago. We go to the same school. I told him hey we still friends and he said yes, but ever since he ignored me FOR NO REASON, he said shit behind my back FOR NO REASON AND he’s the reason people are not talking to me. I seriously don’t understand why, because our relationship was never of cheating or lying or anything bad. We just ended cuz it wasn’t meant to be. But I still liked him as a friend and person. But I don’t understand why he did all that to me, and I’m honestly sad, he was my best friend and then he up and left. I wish he would talk to me but he ignores me... Idc about dating I just miss him and wish some closure of why he said all that. Idk what to do ...