Let me make sure I understand you correctly - you have two jobs, one at a mall, one as...a leasing agent?
In both instances, your boss can elect to ban your roommate from the premises. In the case of the mall store, have your boss notify mall security that he is not welcome in the store. When he comes in, call security to have him escorted out. He has no inherent right to be there, the store can refuse service to anyone.
In the case of the property, it's a bit more of a sticky wicket, particularly since he's your roommate. Have your boss inform him that he is not to come into the office unless it is on actual property business - paying the rent, filing a request for repairs, and such.

