There's quite a bit of weirdness with the roommates. I had the same thing happen. Had plenty of food, bathrooms and they still moved out. I also get these random arguments when there was never an argument. Two sims will just walk by each other then for some reason they are mad about an argument. What??? I think Maxis is just trying to create some kind of drama, but none of it really makes any sense. Same thing with the roommate that drops notes. They'll complain about a messy house but the house is always pristine. IDK. I'm done with roommates until it actually makes sense.