This happened one time my sister came to visit me for the weekend while I was living in college - if I have my timing right, she would have just been 18 at the time. She arrived early evening on the Friday (after having skived the afternoon from school) and we went out for some food and a drink. It was the first time she had come up to York by herself (without our mum) and so she was going to stay in my room. We had a good evening out and visited a few pubs and met up with Mike. We stumbled back to Uni fairly late (although by the time we got there, we had walked off most of the alcohol so weren't really drunk).
I asked her if she minded if Mike stayed over and as an incentive said that she could have the bed and we would crash on the floor (I'd borrowed some blankets from friends and made up a makeshift bed). She agreed and went off to the bathroom to change and Mike's fingers went straight under my skirt and to my pussy. I told him to be quick and sat on the bed. He started to lick me but unfortunatly my sister didn't take very long so I hadn't cum yet by the time she had changed.
I went to the bathroom to change (it's been a long time since my sister and I have seen each other naked - probably not since we used to bath together when we were young). It felt strange to wear a nightdress (have been sleeping naked as it makes it easier for Mike to 'access' certain bits of me through the night. Mike brushed his teeth and then slipped out of his clothes under the covers on the floor (no PJs at my place). I turned off the light and joined him as my sister got into bed and we chatted about what we were going to do the following day. His hand was already under my nightdress and playing with my nipples, but it was fairly dark so I felt quite sure that Sue couldn't see anything.
I felt his cock press against my pussy and put my hand on his side to tell him to wait until Sue was asleep but I was wet enough that he slipped into me (I may have pushed back a bit). I pressed against him and he got the idea not to do anything more though. We kept talking for a bit and I could feel Mike moving very slowly in me (really just pressing deep into me) - after a while Sue seemed to go to sleep (I asked her a few questions that she didn't reply to).
Mike started pumping into me faster and I whispered to him to keep quiet. He reached down and started to rub my clit. I kept listening for any noise from the bed but my sister was silent and I could feel my cunt getting wetter. I knew we'd probably only be able to cum once so I pressed his fingers harder against my clit and pressed back against him to get his cock deep in me. Mike came fairly quickly and was breathing quite heavily but I was close so just kept pressing his fingers against my clit hard and soon came (I think I was fairly quiet).
We settled down to sleep with Mike's cock still inside me and his free hand on my breast (best way to go to sleep as you can always get a quick fuck in at any time before you doze off!) After a while (not sure how long as I was almost asleep) I heard Sue call my name - I was going to answer by Mike put his finger on my lips so I stayed quiet. She called again and then I heard movement on the bed. Things went quiet again for a while. I'd like to think I remember hearing the covers rustling with her hands moving but I don't :( - I did hear her breathing change after a few minutes though and become faster and then a few minutes later a few little gasps. I had felt Mike's cock getting harder inside me again but he said the next day that he didn't want to move and make any noise.
I realised that this meant that my little sister had probably just heard us having sex only a few metres away from her (even though she couldn't see anything) and that she had just cum. Suprisingly, Mike didn't try to do anything else, but I certainly didn't feel him go soft before I fell asleep!
Next post is what happened the following night (still not having sex with her!).
Time to go look at some porn now - if I find anyone cute I'll add some pics here - then off to bed.