There is something so profound about how necro cav relationships are meant to make the necromancer stronger and lead to the cavalier's inevitable demise upon reaching lyctorhood, but every lyctor we ever meet regards the loss of their cavaliers with maddened despair and it inevitably leads to every betrayal against god. The thorn in the side of John's empire is that he can't take loved away and all of his creatures will turn on him for making them try.
Ianthe is the only exception but only because she never truly had a cavalier. She has a sister and she will rather starve herself into an undying death until the sun burn out than eat her sister. The greatest necromancer from the house of gold and greed refuses to do that.
I am not even going to try unravelling the Sixth, that's THE can of worms to ever worm of cans. They saw the stages of grief and said "no, we're going heresy any lysis instead".
