I never knew when I married Helen that I got a Stacey thrown in with the deal. Stacey is Helen's best friend and the amount of time she spends at our house she may as well move in. At least a lodger pays rent. I had suffered a knee injury and I had returned to the gym to strengthen the muscle. Helen told me that I should take Stacey and help her do something about her weight and unfitness. Although Stacey is 5' 9" she must have been the best part of seventeen stones in weight. I had often thought it was a shame as she had a very pretty face and if she lost some weight could be a good catch for someone. Reluctantly I took her to the gym with me. We started off on a treadmill and Stacey was out of breath fairly quickly. So I put her on a rowing machine while I continued my gentle jog. To end the session we went into the pool. To my surprise she swam like a fish. She was a better swimmer than me. I tried to imagine what she would look like without the excess fat. Again to my surprise a month or so in she was still going with me to the gym and she announced to Helen and I that she had lost well over a stone in weight. Amazing the difference between a couch potato and a someone who works out. I told her that she would need to use lots of oils or lotions on her skin or she could end up with baggy skin after she lost weight. She asked was I going to rub it in where she couldn't reach. Helen laughed at me when I went red. Later we made a weight chart and put it on the wall. Over the next few months she continued to loose weight and was even beginning to get some shape back to her body. Even her face looked slimmer. The chart now showed that she was now twelve stone and she announced that her target was around the nine stone mark. Helen was enjoying going around with Stacey buying new clothes and I was astounded how even the style of her clothes changed. She started to wear sexy clothes. In the pool Stacey had a two piece bikini instead of the one piece and although she still needed to loose weight she was starting to look good and at one point I was musing on what she might look like when she got to her target weight, I even got the beginnings of a hard on. One evening we were sat around after a meal and the topic as always was Stacey's weight and how well she was doing, when Helen told her that if she got some sexercise she could speed up her weight loss. I had never seen Stacey with a man or lad in all the time I had known her. Stacey said something about, if only. Helen then shocked me by saying, "you would like to fuck Stacey, wouldn't you?" I thought I ought to be tactful and answered, " If I wasn't married to you my love." The thought of sexercising with Stacey was giving me a boner. I sat longer at the table, to hide my swelling, than I might have normally. Later in bed Helen got the benefit of the excitement she had started earlier that evening. We had a mini party at out house when Stacey broke through the ten stone barrier. As she lost weight Stacy was getting flirty with me asking when the sexercises were to start and Helen would join in with her teasing me. I was now regularly struggling with unwanted erections. Helen joked with me in private saying that she had better watch out if Stacey was causing all my unwanted erections. On the other hand she was getting the benefit of some of those erections. I had bought a few bits of gym equipment and started setting them up in my garage. Stacey's weight loss had slowed right up and she was loosing just half pounds a week. It was beginning to get her down. Helen suggested that I worked with her in my garage as well as at the gym. Although she wasn't loosing much weight her body was changing shape and for the better. Then in the garage, when she was stretching on a weights machine her tits fell out of her bikini top. She had done a further three or four pulls before she noticed that her tits were hanging free. She could see that I was looking straight at them. "Perhaps now you'd like to rub some of that lotion on them," she joked. The bulge in my shorts gave my answer, just before she tucked them back away. Later when I was in bed with Helen I told her about what had happened and what Stacey had said. She asked me if I had wanted to rub some lotion into Stacey's tits. I again had a hard boner and truthfully told Helen that at that minute I wanted to do more than rub lotion into them. It triggered a fantastic fuck fest with Helen, with me keep seeing Stacey's tits in my mind. Three days later we were back in the garage. Stacey had placed her towel and water bottle next to the weights machine along with some lotion. On seeing the bottle of lotion my cock began to twitch at the thought of her tits swinging free. I was sat on my new rowing machine I had just bought and as I rowed I watched Stacey on the weights machine. Within seconds her tits were again free and swinging nicely. Instead of tucking them back away Stacey declared that the top was a waste of time and removed it saying that I had seen them before. It was the toughest session that I had ever had. My poor cock throbbed all through the session. I particularly enjoyed her on the treadmill as her tits bounced in time with her running. Afterwards she asked me to rub some lotion in. I enjoyed rubbing some into her tits but told her no when she started to take her bottoms off. Later I confessed to Helen that I had wanted to fuck Stacey after rubbing some lotion into her tits. I was shocked when Helen told me that I should have. Later in bed I fucked Helen silly thinking about Stacey. Afterwards Helen asked, "Was it me or Stacey you were fucking in your head." I told her it was both of them, which was true. We even fucked Helen a second time which was something we hadn't done for some time. In the morning in the cold light of day, Helen told me that I should give Stacey some sexercise to help with her weight loss. I was stunned, I had just been told I could shag her best friend. The next session was two days later and Stacey made no effort to put her top on. My cock was throbbing in minutes. The warm up session had Stacey stood closer than normal and I'm not sure if it was by accident or design but Stacey fell side ways onto me when stood on one leg. We both ended up flat on the floor and Stacey's tits were inches from my face. I could resist no longer and took a nipple into my mouth. Stacey let out a long groan and took hold of my head and held it clamped to her tit. Her other hand was fishing in my shorts, trying to unhook my shorts from my hard erection. It was a very short time before we were both naked and I was behind Stacey fucking her doggy style. I loved the way her tits swung with each impact as our bodies collided. Stacey groaned and moaned all the way through our fucking. I eventually grasped her tits and plowed into her as deep as I could. We were both very close and Stacey told me to come in her. It seemed like seconds later we went into a state of bliss that felt like it lasted an age. Then we were a heap of body parts on the floor. Afterwards when we had recovered the exercises started and I watched Stacey on the treadmill completely naked as I used the weights machine. It wasn't long before I was hard again and I fucked Stacey again on the bed of the treadmill. After the session I felt really guilty having cheated on Helen. Although It didn't stop me from rubbing lotion all over Stacey's body. That night in bed I confessed to Helen that I had cheated. All she said was, "I know." I must have looked confused when Helen told me, "Stacey told me all about the sexercises," as she played with my cock. I was tired from my earlier sexploits, but that didn't detract from the fucking I gave Helen. Afterwards as I lay thinking about everything, clearly Helen had meant that I should fuck her friend. The next month saw me fucking Stacey at every training session and her weight had started to fall away again. I made sure that Helen wasn't missing out with me fucking her friend. Then one afternoon as we all sat around Helen suggested that I join them in an exercise session, something she had never been interested before. She doesn't need to as she is naturally slim and well fit. We all ended up in the garage. Both of them stripped everything off and I watched as the two of them exercised. Helen's tits were smaller than Stacey's and didn't bounce anywhere near as much, but her arse was screaming at my cock to fuck her. It wasn't long before I had the two of them kneeling on the bed of the treadmill side ways. I was taking turns with their pussies and as I fucked one of them the other was getting the attention of my fingers in her pussy. I eventually came in Helen as I fingered Stacey. Afterwards the girls were on the rowing machine and the treadmill. I could see cum trickling out of Helen's pussy as she moved on the rowing machine. Between that sight and Stacey's tits as she ran on the treadmill, my cock was soon starting to harden again. Helen seeing this had me on my back on the treadmill and Stacey riding my cock as Helen sat on my face and having me lick my own cum from her pussy. Between the two of them it was the toughest workout I had for a very long time. We had many more sessions just as intense and Stacey eventually stabilized her weight at eight stone twelve ounces, below her target. She now looked terrific. The sexercises had moved from the garage to our bedroom and we had many memorable sessions between the sheets. My only regret was that the two of them wouldn't play with each other. They were happy for me to touch, lick, kiss, suck and fuck both of them but when it came to touching each other it was a definite no. Then one Saturday evening Stacey turned up at ours with a man. She had finally found herself a boyfriend. Not surprised now she looked so sexy and fuckable. She told us that they had been having sex for a little over a month when she told him about our sexercises. I was shocked that firstly she had told him and secondly that he was still with her. Kirk and I watched the two of them on the treadmill and rowing machine totally naked. It wasn't long before Kirk was fucking Helen and I was fucking Stacey. We had many, many more sessions that all resulted in a fuck fest afterwards. Then to our surprise they announced that they were getting married. Four months later we not only attended their wedding, but went on honeymoon with them. The first night they spent on their own, but the rest of the time we swapped back and forth. Back home our swapping continued and still happened up to the start of the virus. Now in our thirties My wife decided that it was the right time and soon announced that she is pregnant. Kirk was overjoyed when he rang us to tell us that Stacey was also pregnant. It is such a shame that we are isolated as I would love to have fucked Stacey as her belly swells and no doubt Kirk would have done the same for Helen. Alas not to be. But what we have agreed is that when we are back to some sort of normality we will continue to sleep with each others partner. Only two weeks before I'm due to be a dad now.