I can't stop thinking about my ex bf! Please help!!!?

[Roses3434]

We used to have so much fun together and he used to make me laugh. We would go hangout at the park or go watch movies, until he had changed. He flirted with girls behind my back and held thier hands. Him and one girl took pictures together and on social media people said they looked so cute together. I felt heartbroken. So I told him we were done, but he kept leading me on and telling me he likes me but flirting with those other girls and took that other girl to the prom. I really miss the good times we shared and its been hell trying to get over him because he always stares at me but still hangs out with that girl he took to prom. So when I tried to move on he wouldn't stop following me to my classes. He just hangs out by the door of my classes and just stares at me. When I tried to talk to him about it that other girl kept coming over and was talking to him. He drives her home and they eat out together too. :| I don’t know. I just feel like half of me knows that I need to move on but then some part of me wants to keep hanging on to that hope that we will work out someday. The truth is that I miss our friendship and all those memories we had shared. I can’t stop thinking about him. I have tried to avoid him but he follows me or shows up in the places where I hang out but then ends up with that girl. Advice?