I really need help

My past bf and I ended things on a bad note. He cheated on me and lied about it and ignores me in class. We are not close to being friends and haven't talked since Ferbruary. He started dating a new girl 5 days after me and said to everyone he dumped me because I wanted to me new people, but we talked about it b4 and he still dumped me. He told my friends I knew he was cheating and I was ok with it but i had no idea. He cheated on me with his best friends sister. This guy meant the world to me, he use to hold me, stay up late with me, kiss me, and he was just a loving person,and my first bf. My memories are constantly flowing in my brain and he is always staring at me. I wish things didn't go wrong. Can anyone help me?