I knew my brother's wife Diana was cheating on him. How? We it was because I was the one fucking her at every opportunity. It started after a party at their house. My brother was pretty drunk and I helped Diana to put him to bed. When the party had wound down and all but myself, Diana and Marvin had gone. I helped them clearing up. It had been one hell of a party with nearly eighty people there. Indoors was pretty well cleared up, so I went into the garden with a plastic bag collecting tins. It wasn't long before it was full and I put it with the rubbish and went indoors for another bag. I discovered Marvin between Diana's legs giving her a good licking. I watched for a few moments before Diana spotted me and pushed Marvin away and straightened her dress. No panties I might add. Marvin scurried away and left as quick as he could. I picked up another bag and went back to the garden and resumed picking up tins. I was quickly joined by Diana trying to explain that it was the first time, and she hadn't meant to cheat on my brother. Then she blurted out that he hadn't touched her in over a year. I couldn't understand why he wouldn't want to touch her as she is a gorgeous looking woman. Then she was in floods of tears saying she didn't want to end her marriage but she couldn't stand him not touching her and that women have needs too. Then she had her head on my shoulder crying. Well to cut a long story short, I all but threw her to the ground and was down on the pussy that Mervin had warmed up, and before too many more minutes I had my cock in it and fucked Diana silly for a good twenty minutes. Fortunately we were far enough from the house for anyone to hear her, as Diana was a noisy lover. She grunted and groaned as I fucked her and emptied my ball in her pussy. Then when we both recovered she was kissing me and thanking me for fucking her. We eventually finished the clearing up and I left Diana to go to bed and went home. I felt guilty for the next few days. Then on the Friday night I met up with my brother to go to the pub. As we sat drinking and talking I broached the subject that he wasn't getting along with Diana. Then he spilled the beans. He thought he had cancer. The reason for his assumption was the he had a lump in his groin and it had got to almost the size of a tennis ball and was very painful. I asked him about doctors and he said he had been too shy at first to go as his doctor. The reason being his doctor was a woman, and then as it got bigger he thought he was too late. He became too embarrassed and scared to tell Diana of his fears and hence he started sleeping in the spare room. I disappeared in the toilets with him where he showed me the lump. It was sizeable and the surrounding area looked very painful. Back at our table he said that he wished that Diana would find someone else. I nearly told him about our quick fling. Then he said, "Why don't you take care of her needs. She's a good looking woman and your single." I told him I couldn't as she was his wife and that he needed to go to the doctors and see if anything was able to be done. He agreed if I would take care of Diana. He eventually persuaded me to agree to our pact. I made sure that my brother made an appointment with his doctor and arranged to take Diana out for an evening. During the evening I told Diana why my brother was sleeping in the spare room and that he wanted me to take care of her. We cut the evening short and went back to my house. Once there I slowly undressed Diana and kissed every part of her as I did. She was moaning long before I got to her pussy. When I did it was soaking wet. I licked it for some while before I climbed between her legs and eased my cock into her pussy. We fucked for a long time before Diana came triggering my own orgasm. After resting for some time We fucked again, this time in the doggy position. She later told me that my brother had only fucked her once, in their fourteen year marriage, in that position and it was just after they married. She went wild when her orgasm approached. She was shouting for me to not stop and give it to her and harder. Then we both came. Later I took her home. My brother winked at me and asked if all was well. I told him it was and Diana was ok. I told him I would be with him the following day for his appointment with the doctors. When we got there his own doctor was away and instead there was a male doctor. I asked if he wanted me to go in with him. He told me he was ok on his own. When he came out he looked worried and told me that the doctor had made an appointment with a specialist at the hospital for the following afternoon. I went with him. The specialist wanted X-rays and sent him straight down the corridor to have it done. Then we were back waiting for the specialist again. I went in with my brother as he feared the worse. The doctor told him it was an embolism and could be repaired and the main lump, whilst it was possible that it was cancerous, the odds were that it was benign. The doctor said my brother would get an appointment through the post in the next few days for an operation. He was much happier as we drove home. In doors he told Diana that he would be having a minor operation to repair the embolisms and remove the lump. I had already arranged to see Diana again and told my brother that I would cancel it with her. He told me not to be so daft and that she still had needs and I should go ahead and see her. Well I did and we went straight to my house and fucked like rabbits on and off for over four hours before I took her home. For her first time ever Diana sucked my cock. She had never performed oral sex on a man, although she did admit that she had gone down on another girl in her teens. For someone who had never done it before she was soon up to speed as it were and sucking like a pro. Again my brother asked if all was well and I told him it was. Over the next week I fucked Diana twice more. Then I took my brother and Diana into the hospital and he was taken down to a theater and returned in a little over an hour. He was still groggy and the nurse said all had gone well. When he was fully awake he was in some discomfort and the nurse gave him some pain killers. They told us that he would be staying in over night and would be released the following day. It was then suggested that we let him rest. Diana stayed with me that night. I fucked her on the stairs in the doggy position, and then again in bed with her ankles around my ears and later still face to face on our sides. That was the most sensual fuck that I had with her. Then again in the shower, holding her left leg up as I slammed into her against the wall. Then we got the call to collect him. He was hobbling trying to keep his legs apart. Still very sore by the looks of things. He had several follow up appointments, but he was home. Once home he asked if I had taken care of Diana, I told him I had. He was pleased that I had. Over the following days his walking returned back to normal. and he moved back into his bed with Diana. I felt sad thinking that my time fucking Diana had come to an end. Then she told me that she had booked us tickets to go to a show. It was something my brother wouldn't go to and it involved a stopover in London for the night. My brother gave his blessing. Between the shopping and the show, it was a day and night of fucking and sucking. Back home it was time for my brother's first follow up. The nurse took out his stitches, much to his embarrassment, then into see the doctor. It was good news and the lump was not cancerous. My brother almost cheered. It was the happiest that I had seen him in a very long time. On the drive home he asked me to stop. "I know you have enjoyed seeing Diana," he said, as I sat there expecting to be told now he was ok and that it was now hands off. "I know she has been much happier since the two of you have slept together, so I want you to continue to see her." I was shocked, it was the first time he had actually acknowledged that we had actually slept together, in the past he had only hinted and not actually said so. Secondly he was giving me permission to continue with our extramarital affair. From then on Diana would sleepover at mine one or two nights a week. In the pub one night my brother started a conversation about my affair with Diana. First he thanked me, then he said that Diana was a much better lover since I had been seeing her. He had received his first blow job from her and had thoroughly enjoyed it. They had screwed in places other than in the bedroom, which was another first for him. He was pleased that I had prevented Diana from leaving him and having affairs outside of our arrangement. I hinted about the two of us seeing to her together. From my brothers reply he had no wish to see her fucked or for a threesome, but he was happy for me to continue to see her for as long as she wished. Well that was seventeen years ago and Diana still sleeps over one or two nights a week and my brother is still happy with his and my sex life with her.