A fic where Snape is immobilized - but he and Hermione are forced to have intimate relationships

Hi!

Looking for a fic

I was reading something else and had a flashback and remembered this one.

- Hermione saves Snape in the Screaming Hut

- She does a spell or something and ends up being bound to him

- Snape gets immobilized

- They have to have sex weekly or monthly (I don't remember) - she only visits him then

- Being immobilized, Hermione does all the work in their interactions

- Hermione meets Ron or someone else

- He enjoys the act..but feels bad that Hermione is forced to do it.

-High chance of it being a one shot

-Possibly in AO3

Does anyone remember him?

(I hope I didn't mix up multiple stories)