Whoa. This should absolutely not be as hot as it is. But, DAMN.
There's a lot to love here, but the thing that strikes me the most is the way you've given this a sort of dark, seedy quality, yet at the same time, made it surprisingly intimate.
You've captured Snape in that precise moment where vulnerability and loss of control show through in his expression, in the flush to his cheek, in the way he's gripping Filch's arse with one hand and the door knob with the other. Filch looks almost as far gone himself. They're two exceedingly unsexy men, but in this moment, they're hot hot hot. Guh.
Love the dark quality, the light shining down on them, the, er, fluids, the coloring. Really nice job.