I hate my bf (?)

The title speaks for itself. I’m constantly reminded everytime the THOUGHT of him pops into my head how he cheated on me. Before you call me a loser or a bird I know. It’s my fault for taking him back. But whenever I leave him I always miss him and when I go back I’m miserable. I want to leave. I will leave. I just need to know how to finally let go. I’m genuinely asking from the bottom of my heart please give me tips on how to stay gone. 

Additional context: I’m very mentally ill and I’m working towards getting the help I need. I have autism, depression and my doctors are looking into a bipolar diagnosis.