Liz, first of all...I'm so excited that this was the first story I ever validated on this site. It was so completely and totally amazing, finding words for it will be difficult... but I actually took notes (notes...on paper, with a pen!) while reading so I wouldn't forget to mention the things that really stood out to me, but these by no means are my only thoughts on this story.
I loved how you talked about how the Blacks all have celestial names, except Narcissa and she was the one most obsessed by the stars. The scene under the oak tree, where she accused him of loving her for her beauty and he responded that he didn't pursue her until AFTER he'd seen past it gave me chills. And then when she asked him what his secret was, and he said her... more goosebumps!
When she admitted her intentions to align with Voldemort and he begged her to save herself, that he would not stay with her if she was going to show allegience to all he was fighting against. Her haughty conceit, thinking that he'd give up his beliefs for her, that she deemed aligning herself with Voldemort trivial, the fact that she found it trivial is what will be her downfall. The fact that she didn't have to put up pretenses with him, that she was only truly herself when she was with him makes me so sad.
Then when she watched him transform, and realized what he was and what that meant for her. My heart broke, for her and for him. Your comparison to Beauty and the Beast made me gasp... gasp I tell you.
This is truly brilliant, and I adore it more than words can say.