The handwritten diary is just so fitting, I think, because I can just see Snape hunched over it, scribbling and distilling what he knows no one will ever see, but he feels bound to leave some record of himself. Like the sparse use of color and the drabness and gloominess that seems to come from the writer himself. The story itself told just enough, and even though I'd seen this before, I got that lump in my throat.
I love that you examined the 'human' consequences of someone taking up with the Doctor; you really nailed your genres and prompts, and I know how much time you put into this. The end effect is startling and, for me, will linger for a long while. Great job, Snitch!