I really need advice... I know this is a long story but please I need your help?

Okay so I grew up in a town and before 4th grade I moved away, in 8th grade I moved back to the town. I met this guy and I instantly liked him... He has that "bad boy"/"emo boy" look to him. We started talking and we became best friends. It got to the point where we finished each others sentences. We met in October and by January we were so close we were practically dating. He was with another girl so I knew there was nothing I could do. He had stayed over my house (my mom was there) and so I went over his house the next weekend. We were watching a movie together and he gave me my first kiss, lets just say things hit off from there. He ended up breaking up with his girlfriend and we were practically dating. He told me he loved me and I fell for him. I know how you say a girl my age cant fall in love, that I am too young, but I really did. We texted each other from the moment we got up, till we fell asleep texting. I would open my eyes and think about him, and I would fall asleep thinking about him. He was on my thoughts every moment. I was so happy... I went from a cutter on the edge of suicide to being a happy colorful almost straight A student. In March he called me up and told me he met a new girl and that he wanted to date both of us (I am bisexual and he knew that) he wanted to be in a triangle relationship, his next words were "Don't worry, if she doesn't want to do that I will date her and keep it an open relationship" I told him to fu** off and I refused to talk to him after that. It has gotten to the point we fight whenever we see each other, scream to the point teachers got in the middle of us. It tore our friends apart. I still love him, I feel horrible every moment I look at my phone and see he hasn't texted me... we made up once and then I got upset and stopped talking to him. He replaced me within two weeks of us not talking and I still miss him. I saw him in the hallway and in our flex (its like study hall), He had switched his lunches around so we could have been together... I tried again when we graduated to talk to him again, I even dated his best friend to get his attention... all he does it hate me and I want him back... I miss what we had... I know I should forget him and move on but I can't... I can't let go... How can I get him back? Please help me...