We've never been very close. Our mother got married with our step-father when we both were teenagers. My sister always was his favorite. He's rich guy and my sister always was able to get what she wanted from him. Only recently I found out they were having sex. I found out it started after my mom was hospitalized for 10 months, two years ago. She told me she does it because she debts and this is the only way she can pay them. Well, that might be partially true but I think she also likes the thrill of doing it with her own step-dad, simply because she also asked if I would like to fuck her. Now I know how much she likes it.