One night we had our sister in law slepping with since her husband was working night shift in the taxi and she didn't like staying in the house herself. Their kids were staying over at the grandma of my sister in law. We had been seeing each other on a regular basis and it was all just about sex, nothing more, just sex. She liked the way I treated & spoke to her and the fact that I was slimmer than her husband, who was slightly over weight. It also helped that I had a 7,1/2" to 8" tool which is reasonably thick as far as I am concerned. My wife and sis in law came into the house after having been out on an errand. It was pretty late and I was sitting at the computer doing some stuff. My wife hates going to bed herself so she insisted that I go to bed at the same time which was a pain in the ass as I thought that I would at least be able to grab a feel of sis in law's pussy or a good night snog at least. I told her I'd be through as soon as I shut down my computer. Both girls returned to their respective bedrooms to get changed for bed. My sis in law had borrowed a night shirt from my wife as she didn't have any at our house. I went to put the house alarm on and in walking back to m own bedroom I saw sis in law coming out of the bathroom. I whispered that I'd be through as soon as wife was sleeping. She started saying no way, not tonight, but the thought was in my mind, I wanted some pussy. Once in bed my wife showed no interest in any of my advances and she turned over within 10 minutes and had fallen asleep. She is a pretty sound sleeper and I was pretty sure that she wouldn't waken up. I slowly crept out of bed and slowly made my way through to the spare room. My heart sounded as though it was pounding to get out of my chest, I had goose bumps all over my body and I was attemptng to walk on the top staircase areas which didn't have squeaky floor boards. I pushed the door open slowly in order to prevent any noise at all. The room was dark wit the only illumination being provided by the street light through the drawn curtains that we had in that room. I saw movement on the double bed as sis in law turned to watch me enter the room. I slowly pushed the door to close it slightly to avoid any noise drifting through the house. I crossed the short distance to the bed where as she sat up and whispered is wife sleeping. I said yes and I doubt ( more like hope ) if she would wake up. I moved closer to her and asked how she was. Scared, came the response. I won't stay long as I don't want to freak you out, I said. I moved closer to her, she instinctivel knew a kiss was coming and moved towards me to accecpt it. We continued to kiss for several minutes and during this time I moved my hand across to one of her small but firm tits and stroked her hard nipple. I continued to move my hand upwards and proceeded to stroke her neck lightly. Moving my hand down onto her shoulder, I slipped one strap of her satin night shirt off her shoulder. I broke away from the kiss and movde my head down towards her bared breast. I stuck my tongue out and flicked it over her hard bud. She in turn held my head in place to ensure I paid enough attention to her breasts. I stopped sucking and stood up at the side of the bed with a raging hard on. I located her hand in the gloom and placed it at my cock wrapped in my shorts. Her hand snaked in thorough the fly and wrapped around me. I could feel the heat from her hand encase my cock which was throbbing. She pulled me from the confines of my shorts and bent forward and started licking my cock, before engulfing me in her wet mouth, exquisite I thought to myself at the time. One thing I learned about my sis in law in the time that we had been having our fling, she could suck cock. She was pretty heavy going with my cock as well. I loved having my cock squeezed hard and she loved doing it for me. My wife would start off pretty handling me the way I liked it but would fall away after a few minutes whenever we endulged in sex. I didn't want to take off her nightie in case we were interupted or I had to hide. I've no idea where I was going to hide as there was only space underneath the bed or behind a free standing wardrobe in the corner. I pulled her head from my cock. There was no dissapointment on her face as by tis time I knew where this supposed little session was going. I pulled back the cover on the bed and slipped in beside her. She was hesitant at first but once I worked the magic finger in her pussy, which she claimed her husband never did ( Criminal I thought )she soon relaxed further still and got into the mood. Very little was said between us as considering the circumstances, the less noise made, the better I thought. I continued to finger her until I could wait no longer and made a move to go between her legs. She resited a little but I percevered and soon got into position. I motioned for her to grab my dick and put me in, which she did. I lay there savouring the feeling of her pussy wrapped around my hardness. I started stroking into her but had to stop as the bloody pine bed started creaking. Shit I thought, only one thing for it. I pulle dout, got off the bed and led her by the hand onto the floor. She lay down on her back & I got back into position between her legs. I grabbed my dick to start rubbing it up and down at the entrance to her snatch. She knocked my hand away grabbed me, pulling me in towards her tunnel of sex. I accepted my fate and slowly shoveed my hard on into her. We lay there, staring into each other face, exchanging light kisses and slow pelvic movements. It didn't take me long to feel the build up of energy you experience just before you come. I whispered to her that I'm about to come, she just mouthed to me that I should stay in her and fill her full of my come. I came just after that pushing forward to get further into her. She responded by wrapping her legs over my back & pulling my body closer to her. I lay there for 20 seconds and of course the panic set in at what I had just done. Well not so much that I had just fucked my sis in law in my own house, but the fact that my sleeping wife was only on the other side of the bedroom wall. I moved off of her, slipping out of her. She whimpered that she would sleep with my sperm in her all night as she had always wanted to do that. She only wished that I was able to spend the entire night in bed with her, but alas it was never to be. We still had plenty of other sessions in some different places over the 6 years we were lovers and it was great.