JYMA-054 I had sex with my busty sister-in-law while she was helping with chores during my wife's pregnancy

Three years had passed since our marriage, and my wife became pregnant. She wanted to give birth at her parents' home, so she decided to return there. I thought that maybe it would be nice to have some alone time again, but my wife's younger sister came to help with the housework. The little sister-in-law I hadn't seen in a while had grown up completely and had a great figure, very attractive; though I knew I shouldn't think this way, I couldn't help but look at her as a woman. Thinking about being alone with her in the same house made me uneasy. Then, I saw my sister-in-law masturbating and couldn't hold back any longer...