I think this might be a great example of correlation versus causation, and trying to assign meaning to things. I'm sure you've heard plenty of stories of couple's breaking up, and you find out that they had separate blankets and you distinctly remember the cases it was true and convenient forget the cases that it wasn't.
I would say that stress causes far more breakups... and a lack of quality of sleep either increases stress or makes it harder to deal with stress. So until we see data on this, I would actually guess that people who allow themselves to be uncomfortable for their partner are more likely to break up.