Boyfriend Likes Bestfriend

Hi, my name is Marlyn. I need some serious advice. My boyfriend and I broke up last Thursday. I always thought that he liked 1 of my best friends. When I asked him he would always say that it wasnt true. That I was the only person he loved and no one else. Some time later, things started changing. He didnt called me like he did in the beginning and he would act all weird with me all the time. Like if he didnt care about me anymore. One day I asked my friend to call him and start flirting with him. She said ok and she started talking to him. She asked him if he liked her and he said that he had liked her since first they met. Some days later he asked her out. She said no because he was my boyfriend and I was her friend. He told her that that didnt matter. That I wasnt going to know. At the moment I was really sad. I knew that I had to break up with him. One day, my friend called him. I was listening to everything they were saying. Right in that moment I just got in the conversation. I told him everything. HE didnt say anything. He jus got quiet the whole time. and then he hung up. I miss him soo much. I cant forget about him. I would like to know what to do because I know that he doesnt deserve me but that doesnt change my love for him. Please help me. How can I forget about him?