My girlfriend was on her period, so she didn't let me touch her. She promised to let me have sex with her next week. So I tried to endure until the next week. As soon as I entered the house, I saw a naked person, the body was extremely attractive. I thought it was my girlfriend, so I rushed into sex without thinking much. But after a while, I found out that it was my girlfriend's sister! I was very sorry and apologized to her, but she didn't seem to be angry with me, but instead, she wanted to squeeze out my semen...