Years ago, I was 25, I was with my long time partner at the time. We had been living together for 3 years but just 2 months on our own. Her younger sister was moving into the area and we offered her our spare room. She was 19 and very attractive.

She had been living with us for a few weeks at that stage and I was in the backyard. As I walked back towards the back door, I noticed she was having a shower and from where I was standing I could see her reflection in the mirror so I waited and watched her. I had the perfect view of her body when she got out the shower. I this a few times over the next few weeks.

One day I was home alone and had a shower, she must have come home while I was in the shower without me noticing. When I finished, I walked out of the shower to my room in the nude. Next thing I'm standing infront of her, fully exposed. We got both surprised and apologised.

The next day, I heard her take a shower again, so I went outside. This time I wanted to get a little closer, so I stuck up to the window and waited. She stepped out and looked in the mirror, I thought she looked straight at me and I was caught. I froze, but she just continued drying herself off and then I watched her apply lotion all over her body. After she was done, I told myself to not do ot again as this was too close.

A few day's later, I was by myself again and I decided to have a wank and take a shower. 10 minutes later I heard the door open and I turned around, boner in hand thinking it was my partner. To my surprise it was her sister and I tried to hide my hard on. It took me a second to realise that she was naked, just as she told me, she had noticed me watching her and after seeing me the other week she wanted to have a closer look herself.

She stepped into the shower and started stroking my cock while kissing me. We made out for a while before she crouched down and started sucking my dick. I couldn't take it for long and pulled her up, picked her up and carried her to her room. I threw her on the bed and fucked her hard.

We started sleeping together regularly, almost everytime my partner was out and we were alone. A few months later, we were fucking in her bed and had the door open as my partner was not due back for 5 hours. I was balls deep inside her when I heard a noise and looked up. It was my partner.