Geez, unless you could convince a judge you signed the papers "under duress", or that your ex somehow defrauded you, you'll probably have to live with the situation. Obviously, he lied to you. It's your word against his (unless he put it in writing) that he used the threat of the loss of your community property. But....there have been cases where divorce "agreements" have been reversed, though not common. It would be worth your time and $$ to sit with a good family law attorney for 1/2 hour. For $50 bucks or so, you can get an answer that applies in your state.
BTW: did the house belong to him before the marriage, or somehow wouldn't have been considered community property?