Books series - "My B.friend*s father"

"Mistresses obey. Satisfy. Always want. Will you agree to that?" "Yes. In return of..." "I know your terms. Are you ready to hear mine?". I hate the way he looks at me. It makes my skin tingle. I sold myself out to a powerful man. I became a mistress of a cruel and merciless man. I need money in order to save my sister, and he is the one who's gonna give it to me. I should work for him for two months. I would never agree to this, but I have no choice other than