Oh OP another who has been where you are. At least you are now aware, and I think you know what to do? Do not marry him with ku some good legal advice. Your home will become a marital asset.
When I ended my marriage XH didn't put up a fight at all. It was a relief, but also I couldn't, and still can't, understand how all this meant so little to him that he could let it slip away. He cheated on me which was my get out, it have me something tangible hang it on which everyone understood.
I started reading up about narcissism and an awful lot fell into place. Like you I didn't want to teach my DCs that this was how relationships work. Like you, I had my first DC with a man I didn't know.
It went on for years for me. I didn't leave when I found out about the cheating. I didn't leave when he told me about the other cheating. But when I did leave I felt nothing. He had stripped it bare and there was nothing left. I knew that if I didn't leave then there would be nothing of me left and quite frankly with so little self-respect left, I didn't deserve any better if I didn't go then.
I have my 4 DCs, I have a new man who treats me with the utmost kindness. I had no idea what it was like to be cared for. I am finding out now.
Good luck OP with what you do. If you don't do it now, you will one day when you are strong enough.