I wondered for a second whether I had chosen the wrong end but then my dick slipped straight up her bum, right to the top on the first insertion. I sh...ould probably have started slowly but her arse felt so fucking good and I was hornier than ever. I fucked her arsehole as hard as I could expecting her to push me back to slow me down. Instead she reached her arm around onto my arse and pushed me in each time I thrust into her. My mate was fucking her pussy just as hard and considering none of us. I turned to see my sister Katie staring at me with one eyebrow up. “I said you’re a bitch Katie” and smiled as I walked past her. I turned around to close the door behind me and saw her reaching up into the cabinet for a towel and her short skirt had risen just high enough that I could tell she was wearing a tiny black thong that covered none of her smooth ass and disappeared down into her crack. My cock twitched as, for the first time ever, I saw my big sis in a sexual light and I couldn’t. "Was that Switch?" I asked."Yes," he said."You want your girlfriend to fuck your ass?" I asked."No," he said."You want to suck your girlfriend's cock?" I asked."Yes," he said."That's not a Switch, Roger," I replied."S'ok," he replied."You want your girlfriend to suck your cock?" I asked."S'ok," he replied."You want to fuck your girlfriend's ass?" I asked."Yes" he replied."Are you a sub?" I asked, now realizing where his answers were taking me."Yes," he replied."So, you'd let me tell you what to. I sat and watched for a while I know what your thinking ‘pervert’ but I just couldn’t resist she looked so sexy. After watching a while I noticed I had a huge hard on which got bigger as I watched her oil herself up with some more sun tan lotion. I watched in amazement while she rubbed it all over her body.I couldn’t resist any longer I just had to have another wank, it was even better than the day before. The next day after I dropped the kids off to school I bump into Pooja on the way home we.