Why wont he leave?

Ladies I'm having serious problems. I got married Oct 19th 2018. We separated in November. (Such a honey moon. I know😒) Anyways, I got pregnant in November too. Not sure if the baby is my husbands or not. Had period 19th-24th. Stopped sleeping with him while on my period. When we separated he went back to his Baby Mama. So I started something with a guy friend for a couple weeks who I'm assuming to be the Father more so then husband. Anyways in March 2019(So 3 months later), we got back together to try working on the marriage. He was there the pregnancy, knowing babys probably not his, but by law would be. Now this has been a toxic relationship on both ends. Fast forward to now. We've almost been together a year as of March. I can't do this anymore. Like this is doing nothing but giving me bad anxiety. He keeps black mailing me so I can't leave. I feel so trapped. I dont know what to do. Ive thought about cheating in hope he would leave but I can't find myself to do it. I need advice. 😔 I'm in Michigan if that makes a difference.