Fabulous! So many good things. First: Durmstrang! Durmstrang is always good. I love how you created an atmosphere and philosophy for the school, and yay for giving us a bit of Russia. And Zabini, he was perfect. Always stealing my things! That's a catty line that always gets me no matter who says it. Harry was as confident as I like him, and then confused but then rolling his eyes, like he's so over this. Heh, that was a really good choice to use humour to deal with the ethical mess that was Draco. Preserves the ambiguity. But the descriptions of his anger worked like a charm on me -- felt so real, the single-mindedness and he's so sexy when there's no undercurrent of whininess.
And I loved Draco, I loved that he fell in love with Harry after Harry saved him and I loved that as per usual he doesn't want world domination, he just wants some profit, is that so bad? And I thought both his hatred and love for Harry were true. I love him duplicitous but most of all I loved him when his face sort of fell and he said all petulantly "well I didn't have any plan" and Harry thought was adorable. Such a fun yet poignant way to signal that the characters aren't stock characters and they're human in all their (fun and poignant!) smallness.
Last thoughts: I really loved your imagery, in particularly I could see the house around them when they finally fucked, and I enjoyed their sexual dynamic, from the beginning: Draco likes being kissed. Not kissing, being kissed.