My husband is divorced, and our marriage is a remarriage. He has a child from his previous marriage, who is already an adult. From my perspective, he is my stepson, but he is said to be coming here on a business trip, and since it's a rare opportunity, we decided to let him stay at our house. On the night of his arrival, we had dinner with him while being a little excited, and then went to bed early. In the middle of the night, I woke up and heard some noise in his bedroom. When I peeked in secretly, I saw him indulging in masturbation. I thought, 'He's a young man, so it can't be helped,' but when I saw his penis, my heart trembled. His thing was incredibly big. Moreover, being young, it seemed to be extremely strong and curved... To be ashamed, I haven't had sex with my husband for a while, and his thing is a bit small, but I was satisfied. However, after seeing his thing, I couldn't take my eyes off it for a while. The next morning, both my husband and he went to work, and while I was doing housework alone, yesterday's image of his thing wouldn't leave my head, and I had a sinful fantasy. My secret part, when touched gently, was surprisingly wet, and I ended up masturbating as if I was being fucked by him...