Five years have passed since we got married, and my wife got pregnant. She said she was going to give birth at her parents' house and decided to go back home. I was thinking that living alone for the first time in a long time might be okay, but my wife's sister came to help with the housework. I met my sister-in-law for the first time in a long time, and her beauty and adult charm were stimulating. I knew it was wrong, but I couldn't help but see her as a woman. I couldn't calm down thinking about the two of us being alone in the same house. One day, while I was peeking at my sister-in-law masturbating, our eyes met, and from then on, we started our immoral...