I had a similar situation. I go to a university and brought my dog, a maltese named Tango. My roommate bought of puppy, a shihzu, the shihzu insisted on using the restroom in the house, chewing our carpet, furniture, shoes. It was terrible. Not to be the voice of doom, but the dog continued this bad behavior until she moved. It realy stressed my maltese out, he even began losing his hair. My advice is to be patient and give your maltese pleanty of love to reassure him. We would have eventually gotten the shihzu situated, but he was gone before then. Good luck!