Need to Vent about Relationship

So, I've been with my SO for 3 years now. Last year we decided to buy a house together and also planned to have a baby. We didn't get married first just because neither of us are huge on marriage or wanted some crazy expensive wedding so it just didn't happen yet. Well, everything seemed to have gone down hill since last summer. Rumors spread and he thinks I cheated on him. He even went as far as to ask me to do a lie detector test. At first I was hesitant because I think it's pathetic and I don't believe they are even accurate but I did end up agreeing. Problem is no one will do one while you're pregnant. I'm 37 weeks now about to pop soon! Ever since we've had issues and he's being a complete asshole. He decided to move out and move with his best friend back in January to give each other some space yet we still talked everyday and he still came over all the time. He then started drinking and coming around less. Then one day shows up at our house with all of his stuff. Now one would think that this was because he wanted to work on our relationship but not was I wrong... and I even asked him, are you sure this is the decision you want to make? Because he is quite irrational and didn't even have a conversation with me about moving back in. A couple days later basically tells me that he moved back in to save for his own apartment and his friends landlord was coming around and he didn't want to get him in trouble since he wasn't on the lease. He's been an asshole pretty much ever since and he moved back in over a month ago. I've tried to tell him if you don't wanna be with me, you need to go... but he just doesn't get it! And I don't have any options since we own the house together. I have a daughter from a previous relationship who I have full custody of, a baby on the way with her room ready, and two dogs so I can't just walk out and leave. I feel so stuck. I wish I could be strong enough to make a move but I don't even know what that move is! I'm just so sick of the bullshit and immaturity and don't know what to do :(