My Winnie will follow me everywhere. She follows me to the bathroom, kitchen, outside and like yours, she will guard the bathroom door when I shower. She won't do that for my fiance. She follows him to the kitchen to see if he is going to give her some food.
But my male, Jager, I have to put something up against the door. The lil bugger has already busted down the bathroom door. He thinks its funny to take a shower with mommy.
Probally my fault because I first started giving him baths in the tub, and he LOVES his water.
I just think in your case, your dog feels more comfy following you and your GF around more then your roomie.