Satori and I have been friends since childhood, and I often visit his house. We go to the same school and have always been close. Three months ago, we decided to start dating. When Satori's parents were away, I was invited to her house. Since we spend most of our time at school, it had been a while since I last visited her. Satori has an older sister named Konan, whom I used to be close with. We even used to shower together. Konan dresses very provocatively and doesn't wear a bra, making her nipples clearly visible through her thin clothes, her pink areolas constantly teasing me. She caught me peeking at her breasts. While Satori was doing the dishes, Konan took my hand and placed it on her massive breasts! That evening, when I went to the bathroom, Konan called me into her room to talk. She asked about me and Satori, and if we had slept together. When she found out we hadn't, she seduced me to continue what had just happened. She kissed me, let me touch her breasts, undressed me, gave me a blowjob, and let me have sex with her!!! Since then, Konan has been seducing me whenever she has the chance. I can't even be intimate with my girlfriend anymore because I keep thinking about her. Once, when my girlfriend hadn't returned yet, I went to visit Konan. We had sex together. I suddenly noticed a small ring on the table. It triggered my memory from the past, and I understood why she wanted to be intimate with me. The ring was the one I gave Konan, although it no longer fit her, she had always kept it, treasured it, and kept her promise to be my wife. Despite my forgetfulness, dating her sister, I don't know what to do, but one thing is for sure, I won't leave Konan. I want to stay by her side, care for her, love her, and make it up to her!!!