how do I leave a toxic relationship?

How do I leave a toxic relationship? Every time I try to leave I either have a panic attack or fall into a deep depression and I don't know what to do. He is destroying me mentally. He is controlling and mentally abusive. I can't do anything right with him. Everyone around me notices. I don't know what to do :'( please help me find the strength to leave. I need advice and I need it soon because I'm not sure how long I'm going to last. I am adding anonymously but will add and update if needed. Thank you so much for your help.