The cats don't especially like each other. Our sympathy to this is diminishing, however.

For example, despite living in a rather large townhouse with many rooms, they usually insist upon co-occupying the same area. About six feet apart seems to be the optimum glaring distance.

Last week we took the (much younger) boy cat to the vet for a procedure that required an overnight stay. While he was gone, the (much older) girl cat wandered around the house, aimless and lonely--or at least it seemed to us.

Really, their behavior seems to be approaching that of a cheesy TV cop series, in which an old, grizzled, streetwise detective is unwillingly paired with a young, cocky new partner who bucks authority, and a grudging friendship is eventually formed. We're not so sure this will develop into a loyalty so fierce that one would take a bullet for the other, though. I mean, they're cats.