@Mammacool84
To quote SuperChicken to his sidekick; "You knew the job was dangerous when you took it".
I assume you knew his financial obligations when you moved in together and that you gave them serious thought when you decided to have a child with him. If you didn't, then more fool you. If you did and expected him to change on his own or demanded he change and he said no, well, then again more fool you. He feels he's doing 'the right thing' apparently.
If he's too cowardly to tell the ex that their prior arrangement isn't working anymore or if they have a legal agreement (ie he says he 'can't' sell rather than 'won't' sell), then that's a whole other problem. But again, not one you can do anything about.
I'm not saying who is right or wrong, but the bottom line is that he doesn't have to change to suit you as long as his child with you is adequately housed and cared for. And that child is adequately housed, even if it's 'just' a rental. If you don't like it, then ask him to leave so you can buy yourself a nice 2 or 3 bed house in order to meet YOUR obligations, housing yourself and your child.
Personally 'as a breadwinner', I would never have let him move in with such heavy financial obligations in the first place. Reason number 11343592 to never get involved with a person who has children.