First of all, I'm really sorry to hear about your situation. You gave of your self, your money and energy, and the way he has treated you is unacceptable. You should pursue every avenue you can for child support.
As for the house... I hate to say this, because I know how hurt you are, but I think you have to put that behind you. You should absolutely be reimbursed by him, but legally, I don't know if you can get him to pay you, especially since you're name isn't on the deed. Maybe you can, it probably wouldn't hurt to talk to a lawyer.
As difficult as this may be, try not to waste any more time thinking about him... this was an expensive lesson (from a money standpoint), but now you have your beautiful son and he is counting on you. Try not to let this make you bitter or change who you are. This kind of thing can eat you alive if you let if. Focus on your son and being the best woman you can be... your ex will be sorry he messed things up with you and probably want you back.
Why not take a page from his book and get some roomates of your own to help pay the mortgage too???
I wish you all the best -- you didn't deserve what happened, but leave it in the past and focus on having a great life.