I'm not a lawyer, so this isn't legal advice. For that, you need a lawyer. However . . .
Your husband can contract to sell the home if he owns the home. Whether or not his name is on the mortgage has nothing to do with whether he owns the home. However, that raises the question of whether you're a co-owner and, if so, whether you signed. Again, that's a legal question.
However, don't start off by mucking around with whether you've got a binding contract and lawyers. Contact the Realtor. Say: "We want you to release us from the listing agreement." (Technically, the agreement is with the agent's broker.) If the agent (with the broker's agreement) agrees, then you're released. If the agent says no, then contact the agent's managing broker. Say: "We want you to release us from the listing agreement." The broker may agree. Or the broker may suggest you use someone else in his/her office. Or the broker may say no. If the broker says no, at that point, contact a lawyer.
Hope that helps.