oh, how I love this story.
Where to begin? your lovely turns pf phrase? the suspense, the twists of the heart, the beautiful obsessive longing... ahh. The satisfying hot sex? and the comedic turn of the mirror, wonderful!
It's a well paced little mystery, very noirish at times... I can see all the shadowy settings.
As I neared the end, and realized what Snape was going to do, it was all I could do NOT to cry out, "No! you fool! Don't do it!" But of course he did, he would.
The image of Severus as the guardian angel is quite dear to me... he has indeed become one of my beloved companion spirits.