Puppy refuses to go to the bathroom when I'm at work

So, my girlfriend and I live together and I have to go to the office for some of the week and WFH the rest of the week. I mostly take care of our puppy, Nemo, when I'm home, but when I'm gone, he's been freaking out and acting very aggressive with my girlfriend and everyone else, and he acts fairly destructive. We thought it was separation anxiety, but when left around others besides my girlfriend he's fine. We've narrowed it down and think he's cranky around my girlfriend because he won't go to the bathroom when she's around. I tested it by having Nemo go pee and then having her walk in mid-pee -- he stopped peeing as soon as he saw her, and then refused to continue peeing till after she left. He's fine urinating and pooing around others, so any ideas?