SS/MM forever!
I love so many details about this as well as the whole thing - his shirt, his gaze, her bliss, the wine, the rosy-red squishy velvety-ness of the furniture - the color of sex! As seen. As Severus is seeing - he can't take his off it. And then there's the wallpaper pattern, an endless repetition of the pretty shape of a vagina - or maybe also a woman's nipple with its aureole. WE CAN HAZ FREUDIAN HOGWARTS NOW!
But no one has yet commented on -- Severus's feet! OMG! Allow me to rhapsodize on his long, narrow feet and how they curl with pleasure; the way the right one is so arched, while the left one seems to be rippling and wiggling in counterpoint to his and Minerva's movements. Even his toes are squinched up with concentration! It gives away how intensely he's focused on what he's doing and how much he's loving it.
Every detail of their bodies is so expressive of their emotions and the intense complexity of this for them. I just love that. Sex is so not simple ... especially for this young Severus Snape, shagging his teacher!