If he's your EX-husband, then you must be divorced, and you must have a decree of dissolution, right?
What does the decree say?
If it says the house is yours, and it doesn't contain any provision that gives your husband the right to occupy it, then he doesn't have any more legal right to stay in your house than I do. You can call the police and tell them to get him out of there.
If the decree gives him a right to occupy the house, then you'll need to move to modify the decree on some basis. You would need to go to court to do this, which doesn't absolutely require that you use a lawyer, though that's ordinarily a very wise thing to do. The obvious course would be to go back and talk to your divorce lawyer.
