This is how I see the whole bit about Disiri.  Disiri straight out tells
Able that she would eventually tire of him should he walk off with her.
So by her nature she cannot love him as he loves her. So Able knowingly
throws himself away for someone who probably won’t even appreciate it—at
least someone that couldn’t before he sacrificed himself. Certainly she
did come to love Able as Able loves her; Able rising her to human made
her able to, and probably the act itself helped too.  Earlier someone
said that one of Wolfe’s themes is love driving us to become better.
Well, I certainly agree with that. Able’s love for Disiri makes him a
knight and raises him from Mythgathr to Skai to Kleos. He gets to Skai by 
being a superb knight, gets to Kleos by being a good Christian, out of
love sacrificing himself for people undeserving: as far as he knew he
lost everything by breaking the Valfather’s oath, but to hell with it, he 
wouldn’t let people die (even though he was higher than him and they
didn’t deserve his help). It seems that Wolfe is setting up a hierarchy
of good people. Earlier someone setup a cosmology of virtues, and this is 
sort of in that line: we have Berthold, who will throw his life away for
those dear to him; we have a knight, who acts to duty, will throw his
life away for duty; we have Christians, who out of love for humanity
throw away their life for those undeserving. At each level love is
further abstracted. It is easy to love your family, harder to love
something like an ideal, yet still harder to love those unknown to you.

-bruce