Why won't my ex boyfriend give my stuff back he broke up with me?

I'm assuming that you both lived together. If you had a rocky relationship or it was an abusive relationship then he's mean to the bone and he's getting even with you by not giving your personal contents back. If this is the case then ask for police assistance or take along your father, brother to get your personal belongings back. Whatever YOU came into the relationship with such as clothing, dishes, utensils, furnishings, etc., and any gifts he has given you are YOURS!