This made me cry. I have such a childish weakness for cat!Snape that it's really embarrassing. And Harry and his losses and the way he dealt with them broke my heart. From the moment on you chose to write the cat as a Russian Blue (and I always was fond of blue cats and their temperament) and not as a say, black cat, I knew you would handle the whole cliche brilliantly! Pay hommage to it, gently make fun, play with it in a creative way, but never merely repeat it.
Also, your Snape was perfect to me. How I loved the moment when he tells Harry that he is causing the fog. He is the only one who can reach Harry, the only one who understands Harry's pain.
(And also, I loved the sex! It was different and lovely and tender and yet incredibly hot!)