Baby daddy leaving advice

Me and my baby’s father split up around 20 weeks. We was somewhat working on things up until about 4 weeks ago when he slept with his ex. This ex ruined our relationship, he knows she will not be in my child’s life. We have been arguing non stop for a few days and I’m just over this. I’ve been doing everything by myself since he left.. he’s basically living with her now but lying about it. How do I move on? How do I not let what he does affect me anymore? Of course I’m broken from how he’s treating me & I know I can’t change how he feels about me or his actions either. Everything just seems so hard right now. I need help paying my bills and getting the rest of the stuff for the baby but I don’t even want to ask him anymore. Any advice?