My Mate's Father Wants Me

He's my mate's father and I had a one-night stand with him. I shouldn't have but I was just so bitter because my mate was sleeping with my half-sister.
That night marked the beginning of his insane obsession. And then I realized he wasn't the level-headed and calm father-in-law I always thought he was.
Behind that mask was an obsessive, manipulative, and controlling man who had sworn never to let me go. He'd do anything to keep me, including ruining my life.
Now I'm stuck in this clandestine erotic relationship we have. And each day, I find myself getting more addicted to him.
What do I do to break free from this erotic but toxic bond we share?