Going to his girlfriend's house to play young man fucks his girlfriend's sister

Today is the first day I went to my girlfriend's house to play. She lives with an older sister but today she is absent because she has to go on a business trip. I was chatting with my lover when she suddenly came back. It turned out that due to a mistake on the part of the partner, the business trip was canceled. I don't know if by accident or by accident, she brought her beautiful big round buttocks in front of me when my girlfriend went to make tea. That night, the image of her perfect buttocks kept popping up in my head, making me unable to sleep. I wanted to have sex, but my girlfriend wouldn't let me, and I was thinking about going to the bathroom to deal with it, when suddenly I heard a moan coming from somewhere. Following the moaning, I saw that Arisu's room was open, and when I looked inside, I found that she was masturbating! I officially got to admire her beautiful big ass! I was engrossed in watching when she also discovered me. But instead of getting angry, she dragged me into the room, allowing me to kiss her and make love to her! Unlike my girlfriend, she lets me have sex with her whenever I want. And from then on, we kept secretly having sex with each other while I was still preserving my relationship with my girlfriend...