Sorry that your ex is being such a jerk. You really don't owe him anything and at the most I wouldn't pay for anymore that your 50%. Exactly what is going to happen with the house? Once you leave will he be able to afford it? You are putting in the divorce papers that he will have to buy you out, right?
From what you've written it does sound as if he's being petty while looking to get as much out of you as he can. Stick to your guns and consult your lawyer before you give in to anything. It sounds as if he's already gotten a free ride for way longer than he should have.
