A very fresh premise, and the hint of anxiety in Narcissa as she leaves him to go to Knockturn Alley felt very real. I understand your overall message, but the last sentence was a bit abrupt. The meeting did not really build to a climax such that he would be "preparing to live a lie" with such finality.
the story reads nicely (the changes from one situation to another aren't abrupt, which can happen sometimes). i'm not sure that i believe the characterization of harry and draco though. i can't picture harry leveling an ultimatum like that at the end, and draco has too many demons to be unconditionally warm.