M and I have been together for 14 years, she is 11 years younger than me. Since the birth of our daughter we have just existed, very little sex, arguing, like a million other "normal" couples I suppose, despite this I thought we were fairly contented and M was very happy with her lot. Desperate for a shag I posted an ad, photo and all, on S/H but without any real success. I have had a couple of sexual encounters during our time together but took care not to let them get complicated. All unknown to M of course. About 6 months ago M decided she wanted to improve herself and joined an evening class with her friend Tracy. The more she went the more she seemed to enjoy going. I didn't mind as we didn't do anything much together anyway and it gave me an evenings peace.The class finished at 9 and M and Tracy had got into the habit of going to a pub in town for a girly chat usually getting home at 11.30 or a bit later. Life ticked by as normal until I accidentally opened M's underwear draw and found some very nice new looking frilly knickers, further investigation revealed quite a few other articles, including matching suspenders and bras, shorter skirts and a half empty in date large packet of condoms hidden in an old hand bag. Quite honestly I was so shocked I didn't know what to do, I still half thought it must have an innocent explanation.It took a while to dawn on me but I realised that M had started putting on make up for her classes and progressively changing how she dressed, it was so subtle that I hadn't really notice the changes. The following week I feigned having to work late on the night of her course and swapped company cars with a work mate under the guise of picking up some flat pack units (he has an estate) I staked out the school car park where the course was held. Dead on time M drove in and Tracy soon followed, they both went into the building, I settled down to wait, however they both reappeared after about 10 minutes and got into Tracy's car and drove off, I followed them to a local car park where they parked and got out of the car. They both went to another car parked in the shadows 2 men got out and the girls walked straight up to them and kissed them they got in the car. I saw Tracy in the front lean over and kiss the driver hard, I couldn’t see M in the back. They drove off and I followed, they pulled up in front of a small terrace and went into one of the houses. I got out of the car and crept round the back to find an alley separating the rows of houses. I counted which one it was and carefully opened the gate and crept up to the window, through a crack in the curtains I could see Tracy on her knees giving a firm hard cock a damned good blow, and at the very edge of my vision I could see a mans arse driving hell for leather back and forth into a gaping soaked pussy that was flanked by a pair of black stocking clad legs, he pulled out (he was rock hard and quite big!) and the pussy turned over and the cock drove into it like a piston. I glanced back to where Tracy was to see another pair of legs with knickers round one ankle with a mans arse in between pumping for all his worth. I couldn’t believe my eyes, it seemed to end with both men jumping and pumping together. After about 15 minutes of inaction they seemed to change places and it started again. This time the face giving the blow job to a shiny, spunk covered cock was M. I witnessed another session after this where both men seemed to fuck the same girl but by this time all the woman was wearing was stockings so I couldn’t really tell who it was. I was disgusted to find I had a huge erection myself, after all is was my partner in there being screwed! Eventually they all stood up and with a bit of frenzied dressing they went to leave, I ran from the garden and got back to the car just as they came out of the house and got into the car, they drove back and dropped the girls off. I drove to where Tracy lives and waited. About 30 minutes later she pulled round the corner. I got out of the car and flagged her down, the look on her face was a picture, I told her to follow me to a local picnic spot where she got into my car. After a bit of half hearted denial and some bravado she told me that she had seen my add on S/H and jokingly told M, they had flirted a bit with a couple of lads in the pub after the second evening class and in the light of the revelation decided to take it further. Apparently M was very pissed of and frustrated, she fancied some no strings fun to. They had been seeing guys once a week, getting changed into sexy undies in the school toilets, sometimes some of their mates came along too and they had four and even more somes. I was right and it M was being double fucked tonight. They had a string of young lovers and found it easy to get as many as they wanted. She had even had girl on girl sex with M. She asked what I was going to do, she was terrified I would tell Dave her husband, after establishing that she and M were really only doing it for sex and there was no risk of her leaving me I said nothing, what could I say she was just doing what I had done. I did however tell her that she would now be at my beck and call, she agreed and I reached over and peeled of her soaked knickers and rolled on top of her, I released my stiff cock and slid it straight into her spunk soaked pussy and soon added my own juice to her wetness. I now have a sex slave to die for who will do pretty much anything I ask. She also makes sure the curtains are open at the house when they are having a session. She calls me and tells me if there are any special things arranged. And always describes what she and M have been up to if I can't make it. I am writing this as a warning to all the complacent blokes out there, if you are going to play away be prepared for the revenge if you are caught, it is very hard to deal with!!