I have recently been fucking my sil while she is staying with us due to her work placement away from home. My wife (34) and I (35) live in Kent, we both are doctors working at the local hospital sometimes different shifts. We are very open minded and have experimented in swinging and at a few times dogging at a local place. I guess it keeps our relationship stronger and boosts our sex life. We are both very sexually active. My sil recently finished her medical studies and I managed to get her a work experience at the same hospital, pulling a few strings. She is 26, blonde, has a very toned body and with a 34DD chest. Due to costs we agreed to put her up in our spare room. I've known her far a few years and met her various BFs. She is very good looking and at times I have thought of fucking her. With the recent hot weather, I have seen her half naked body many times and it has turned me on. She has caught me looking at her boobs, legs and bum. It all started one particular Monday morning. I was on my day off and while laying on my bed heard a few moans next door. I walked out and crept to her bedroom , which was slightly open. I saw her laying on the bed all naked, with her legs wide open, eyes shut and playing with her rabbit in her shaven pussy. The speed and buzzing noise drowned my foot steps and she continued to ramp the vibrator on her cunt, occupationally teasing her clit with her other hand and fingers. She seemed to really enjoy her self and was also playing and squeezing her enormous hard nipples. My cock had shot up like a rocket and it was throbbing. I just wanted to enter and play with her beautiful body and make her feel the real thing. I resisted, went back to my room and started to wank myself thinking of what I saw. Later that morning, I was making a coffee still in my shorts, she came downstairs in a very short night dress and was surprised to see me. I explained my day off and she somehow seemed embarrassed. I made her a coffee and we sat on the dining table , me just in shorts and her in her very see through dress. I could see her breasts and the nipples started to get harder. I started to develop a semi. It became very visual and she clearly saw it and couldn't keep her eyes away from it. Feeling horny, I said 'looks like your still not satisfied'. She realised what i meant and said 'the real thing is much better'. I moved towards her and she responded with a long deep snog. Her tongue was way inside my throat and she very quickly moved her warm hand on my cock and started to stroke it. She moved my shorts away exposing my rock hard cock and started to wank it. I opened her dress and started to play squeeze her nipples and her gorgeous breasts. Moving hand down to her legs leading to her wet pussy. She moved apart and I got a deeper entry and started to finger her. She was moaning heavily. I picked her up and took he to the large leather sofa in the lounge. Opened her legs and started to lick her young pussy, flicking her clit and then tongue fucking her. She responded by saying' fuck me deep'. I lifted her legs on my shoulder entered he in one deep stride and continued to fuck her deep and at a fast speed. She moaned with pleasure. It was not long when she screamed her head off while releasing her juices all over cock. I continued until I felt the sensation of my spunk filling her hot pussy. We cuddled up to each other , kissed and stroked each other very tenderly. She whispered' I don't need my rabbit anymore'. It's been three weeks now and we have fucked each other at every opportunity.