I was going out with a twin who had a very high sex drive. Both girls had long straight brown hair, pretty faces, 34B breasts, slim bodies and long legs. They were 17 years old and stood at 5' 7" and looked completely identical unless they were naked. One had a mole. We had been watching TV with their mother and younger sister. It was getting late and it was time for me to head home. Her twin had already left the room and I assumed that she had gone to bed. Their mother was aware that I was having sex with my twin as they discussed everything. As I got up her mother winked at me, knowing that in the hall way we would kiss and cuddle before I left. In the hallway as usual I had my hand up her dress and in her very wet fanny as we kissed. She was stifling the moans as I finger fucked her. My cock was rock hard. I decided to turn her round and lean her over a cabinet and fuck her from behind. I slipped straight in and was working her fanny over, when I noticed that her sister was stood just two treads up the stairs from us and watching her sister being fucked. Then she came down the two steps and bent over the cabinet next to her sister, raising her dress revealing that she wasn't wearing and panties. I slipped out of what I thought was my twin and slipped my cock into the other twin and gave her about ten pumps with my cock. Then back to the first twin. After about ten minutes I asked which one wanted my cum. They both answered yes they did. I thought to be fair I ought to give it to my girlfriend, so I asked which was my girlfriend. They both claimed to be my twin. I was so close I just picked the first one who I thought was my twin and slammed home and unloaded into her fanny. I pulled out and was putting it away as the girls straightened their dresses. They both kissed me goodnight and I left for home. The next night I took my twin out to a pub where we had a few drinks and then I drove her to a very quiet lane that was used by courting couples. We were soon in the back seat and as I was about to fuck her I noticed that there was no mole on her thigh. This was not my twin. I was rock hard, and as they say any port in a storm, I slipped my cock into her willing fanny and shagged her long and hard. As we sat talking afterwards I asked how long had they been sharing me. She told me from our second date I had screwed her. From then on they took turns sharing me. She told me as her mother was unable to tell which twin was which, she had no idea as nor did I that they were playing shares. I asked who got my spunk last night and it turned out that my twin did. I told her that now I knew that they were happy to share, the first opportunity I was going to screw the two of them as they played with each other. She said that she was more than happy to do a threesome with her twin and she would let her sister know. It was not long after that evening that I managed to organize a complete night with both of them. That's for another day.