The girls were paid and sent home. Danielle and I were tired. Soon I got a panic call from Tiffany; her sister wanted to see me. Now! As soon as they ...ung up they were on their way. I panicked but Danielle calmed me down.When the girls arrived Danielle brought them straight to my room. I knew Tiffany’s sister Sherri from grade school. Sherri was my age but a year behind me. She looked real pretty too. I was expecting her to threaten me but instead she wanted to become one of my girls. What!. " She actually used my name. "Can we rub out that last sentence please? It is me that needs help. I'm so sorry for what I said. It came out without thinking."Okay, let's start again. Why do you want me to help you?"She hesitated and then repeated her first statement. "I still think the tutor is shit. It's okay for people like you who more or less know it to start with and only need a bit a revision, but for those of us who haven't the background knowledge, he expects us to pick it up from. At this time I could make out the outlines of her nipples through her shirt. I pulled Pammy close and went for it, I kissed her right on the lips. She didn't move away and actually kissed me back. Soon our tongues were exploring each other's and my hands found their way to her ass. The song ended and we went and sat down in the corner booth. I wasn't sure what was going to happen, but I knew what I wanted to do. We sat down and we started making out just like we were in high school. Her hand. Almost as if she read my mind, she reached back and grabbed onto my side and pulled me in tighter until my dick was forcefully pressed up against her ass. Her perfect round ass that I had only ever snuck peaks at was now grinding up against me. It drove me wild and I wanted nothing more then to grab a hold of it. To squeeze and slap it and have all my expectations met but…I couldn’t.She was my sister.“S-Stop,” I whispered softly, my voice felt like it was fighting to stop me from doing this..