Looking for story about younger babysitter and older husband

[SweetAlpaca]

I'm looking for a story about a teenage babysitter who's attracted to an older guy. He and his wife go out but he comes back early and they fuck in the house's gym room. He's very dominant, blindfolding her, not letting her touch herself and ordering her around, and after they fuck he offers her a job as his personal secretary or something. The story ends with her finding a collar and the guy saying something along the lines of "you weren't supposed to see that yet".

Thanks for the help!