Three years after we got married, my wife became pregnant. My wife decided to return home, saying she would give birth at her parents' home. I thought it was okay to be single for the first time in a while, but then my wife's sister came to help me with the housework. I met my sister-in-law for the first time in a long time and she seems cute, has a good figure and is attractive, so even though I think it's no good, I see her as a woman. I don't feel at ease when I think of being alone in the same house. At that time, I saw my sister-in-law masturbating, and I couldn't resist it and approached her. After that...