I love the idea of Snape interacting with Harry in dreams, behind his occlumency shields. The truly amazing part is your characterization of Snape, though.
There are so many little subtle keys to Snape's psyche in this inner monologue that I can't list them all, but this one sentence made the entire story come together for me:
"... in his dreams I have shaped him to be without remorse, answerable only to the logic and morality inside his head, a morality that is as rotten as my own..."
Can't seem to reread that bit enough times.
In just over 4000 words, you've included a very original idea, a plot, hot sex AND a very nuanced sketch of a dark, complex character. Your Snape runs deep, he's twisted in but a way that makes perfect, tortuous sense, you draw us completely into his mind and POV. I think it would take me more than 4000 words to spell out everything you've revealed about this Snape through nuance and detail. Bravissimo!