No, you don't call the police. They will not get involved in a matter like this.If the final agreement (such as agreement you entered into after mediation) or decree/order in the divorce states that it is only for his and the child's use and he is now in breach of it by having a roommate, you can file a motion in your divorce case to enforce the agreement or decree: the court can order the roommate to leave and/or assess some damages (monetary penalty) against your ex-husband.If the above never actually made it into the final agreement, decree, or order, however, but was merely something the two of you discussed, then he can have his roommate there as long as he remains part or joint owner of the home.