Mentor (Impossible #5)
Julia Sykes

A beautiful, nameless man took me. He wants to break me and make me his. He treats me like his plaything, but I suspect I mean more to him than idle amusement. The monster needs me.
What's truly terrifying is that I'm coming to need him. He sets my body on fire, and I crave his touch.
When trapped in the dark, the blacker shades of lust can be confused with love...
Note: Mentor is part of the Impossible series, but it is standalone story. It is connected to Knight (An Impossible Novel), but it can be read before or after that without anything being spoiled. Mentor is a 33,000 word novella.
Impossible Series Reading Order:
Impossible: The Original Trilogy (Monster, Traitor, and Avenger)
Savior (An Impossible Novel)
Knight (An Impossible Novel)
Mentor (An Impossible Novella)