This is really good. You've created such an effective voice and viewpoint for Abraxas; he's just exactly the sort of man I'd imagine a rich pureblood to be: (to his mind) eminently reasonable (and not superstitious at all, of course not), with a view of gender that he no doubt sees as simply a reflection of nature, of the way the world is. His upper-class notions of taste and discretion and tradition seem spot-on to me. I love seeing Regulus and Rabastan through his eyes, too.
It would do them good to remember that someone was always watching. Perfect Abraxas touch. And I love that he finds the Dark Lord tacky -- ha! Half-blood parvenu; what else would one expect?
It would not do for the youngsters to see that he, too, was capable of being startled. Another perfect touch.