What do i do!? boyfriend helpp. guys maybe answer? girls too i guess. someone just help!?

ok so my boyfriend thinks i cheated on him, which i did not do. i love him with all my heart and to be completly honest i would have never thought that anything or anyone would come between the two of us. everytime we try to talk it never works out, either he ignores me or we end up back in another arguement. well then on thursday we broke up and on friday this girl comes into my homeroom and looks at me and says "you know my cousin right? we do you know his friend ____" (my ex) so i say yeah and she tells me how he would not stop texting her all thursday night and how he wants to pick her up from school and how he keeps asking if he can come over her house and tells her how pretty she is and blah blah blah. its been one day, what is that!? so i text him and he flips out on me telling me im a ******* retard and not to ******* talk to him.. ok how is this my fault again? i didnt cheat on him thats the last thing i would do. i know what that feels like. he used to tell me how much he loves me and how much being with me was the best thing he ever choose and all that. i really thought our relationship was amazing and nothing would ever tear us apart. what do i do now. should i try to talk to him still or should i just leave him alone. i dont want to move on. if i wanted that and i didnt care then hearing what that girl told me wouldnt have hurt so much.. ugh someone please help me!