Your husband needs to know you are paranoid. That alone can ruin lives. Look into either slowly paying your mother in law back or "work off" the money. Turn all money/cards/ checks over to your husband you never get them back but you get a % allowance, unless your husband trusts you with it. Possibly your keys too.

Explain that this is an issue between you and him bringing outside people in just makes things worse. He needs a therapist, you need a therapist, if you have kids they need a therapist , and couples therapy is a must.