I fell inlove with my teacher and he screwed me over. What should I do to move on?

He's 26 and I'm 17. I started in this AP physics class and it was really hard and I failed every test in the first 3 weeks. This teacher attempted to kick me out of this class but he also offered tutoring me. He seemed very patient and friendly. We went on school trips together and talked endessly , I began to improve alot and became one of the most prepared in that class. As time passed I became closer to him , I would talk to him about anything and everything. We both felt attraction for each other and there was an imminet desire to spend time together. Our eyes connected in every possible chance. One night I hugged him at this school event and we stayed locked for a long time. We never told each other anything but we knew what we felt. He's engaged , so I was desperate to move on , so I began dating someone to forget him and I couldn't but instead I had started major rage from this teacher. He was angry , he was jelous. I remember having many arguments over stupid things just to let the anger out. So I realized I was going nowhere with this relationship so I ended it. Things were hard for us. He was still angry,and I was still dumfounded by everything. We kept working together and the love came back and we continued to follow this feeling we had a few set backs but we came back to each other. Sometimes a stare , would be all that I had , all that we had to show that he needed each other , that we loved each other. I joined a sport he coached so we could be together longer but things started to change. He changed , he became cold , angry and impatient with me. He began to slowly drift away from me. I realized and began to depart as well , I didnt try anything to get back I thought maybe its time to do things right. But suddenly I noticed him , falling for another STUDENT , he is flirty with her , he follows her around in practice, and smiles at her like there is no tomorrow. He basicly traded me. What should I do? How do I move on ? What do I do in practice?