[While he's not quite above endless bickering that loops in circles, he sighs and decides that he might as well attempt to be the mature one here. Since he's already cleaning up after her and all.]

Look, I don't know how things are where you come from. But where I come from, it would be improper for a man and a woman to live together unmarried — or even spend time together unsupervised, for that matter. Maybe it is old-fashioned, but that's what I'm used to. So can you at least try to understand why this makes me uncomfortable?

[He feels a bit foolish having to explain, but it becomes easier to talk to her when he can focus on straightening up instead.]