Advice on how to move on.

I started dating this guy towards the end of freshmen year and we were on and off from then up until junior year. To be honest it was my fault we were always on and off but I dont want to take on full responsibility. We had horrible communication skills over the phone but in person we were fine, we had such amazing chemistry and I honestly thought wed last long but once we stopped seeing each other in school and we didnt talk much on the phone I broke up with him cause, I wanted him to fight for me so I took a drastic step. In the long run it didnt work out, hes moved on and I havent and I see him in school all the time with his new girlfriend and I try and try to pretend Im okay, but Im not. Seeing them together literally makes me want to cry and I dont know what to do. I dont know how to move on.