For me you hit the nail on the head. It is a fucked up relationship, its an extremely complex one as well. The two would literally, and I mean literally due anything for the other (and over anything or any other person (s)), but it is seriously whacked.
And if they actually did open up and talk about the issue that come up, about 40% of the drama between them would be taking care of. But they don't really talk about their problems.