Welcome to YT . First of all male yorkie's are nortious leg lifters. Especially when they are not fixed. first thing to do is get him fixed ! Anther problem is that he is in a new invironment. You guys allowed him to have free reign of the home. If he was not potty trained the he needs to be confined to a certain area. PLace him in a Ex pen, or start crate training him. He can't have access to the whole house.
Is this new behavior? Was he trained before your GF moved ? If the yorke was trained then this is behavior is caused by the stress of the move. However it still need s to be dealt with propperly.
The Yorkie should never be swatted ever. This is causing fear agression . He is responding very negative , from you hitting him. Of course he will want to bite anyone who is going to hurt him. Please stop hitting this yorkie, it is making things worse. And it is not how you train a dog.
DO not let the dog sleep on the bed either. Keep him out of the room all together, and give him his own bed somewhere else in the house. Along with pee pads.
Let your girlfriend handle the Yorkie instead . Because the yorkie is aggressive towards you, and it is not a good situation right now. He is scared of you because of the hitting. This behavior is not going to go away, until you regain his trust.
Under no circumstances should anyone hit a dog.
