Donna and I bought a caravan and sited it on the Gower for the summer. I left Donna there with plenty of food and drink and the caravan was set up and plumbed in. She has not needed to work since we married and I am happy for her that way, so she could spend the whole summer enjoying herself and keeping up her suntan. I would get down to her most weekends for a few nights and replenish the food and check on the caravan and do any maintenance that might be needed. Bob the manager on the site said he would kept an eye on her for me. It was about six weeks in and I took the Friday off work as there was virtually no work in. I got to the site about 9 p.m. on the Thursday night hoping to surprise Donna. As I turned into the site I could see my caravan. I stopped for just a second as someone passed me coming out. It was now that I noticed that my caravan was rocking. I had to take a second look and sure enough it was definitely rocking. For a second I wondered what Donna was doing to cause it to rock. I pulled into a pull in and just watched. About three to four minutes later the caravan stopped rocking and after another few minutes the site manager Bob left my van. It was quite obvious that he had been taking care of my wife. He was keeping more than an eye on my Donna. I slowly rolled down the hill and as I passed Bob smiled and waved at me and told me he had just changed my gas bottle for me and the empty was in the awning. I almost asked if my gas bottles were kept in my bed. At the van Donna acted as if nothing had happened and I started to doubt what I had seen. We had a nice day and later on I took the rubbish up to the bins and as I sorted out some bits for recycling I spotted several condom wrappers in with our waste. My eyes hadn't deceived me, it was Donna and Bob that were cheating and not my eyes. Worse still, while he was shagging my missus, his own was just a short way further up the field, I assumed blissfully unaware of her husbands infidelity. We had a great day on the beach and wandered around the few shops that were there and later we changed and went to the pub for some food and drinks. Donna drank a bit more than she normally would and got just a little tipsy. We staggered the short distance back to the caravan and were soon in bed and starting to make love. I'm not sure if it was because of what I had seen, but I was extra hard as we started making love. I kept getting this vision of Bob on top of Donna. Then it happened. Donna suddenly blurted out, "Fuck me Mac. Yes harder." I stopped and looked down at her, "Who the hell is Mac?" I asked. I could see the look of fear in her eyes. I had climbed off of Donna and was sat next to her, "Well who the fuck is Mac?" "I'm sorry. I didn't mean to," she said quietly. I pressed again and she blurted out that he was the guy in the caravan on the level below ours. She owned up thinking It would result in an argument and ultimately divorce. Divorce was the last thing on my mind, as my cock ached, as she told me that she had been sleeping with him. She told me that she had slept with him five times. I was shocked that it wasn't Bob and asked her about him. She told me that Bob had caught them sleeping together. Then the bastard was blackmailing Donna and told her if she didn't let him fuck her as well, he would tell me on my next visit what my wife had been up to. Instead of getting upset with her I turned her over into my favorite position and fucked her long and hard knowing she had been fucked by not one but two men in my absence. I was pretty sure that Donna enjoyed the extra hard fucking. The next morning I told Donna that I didn't mind so long as she told me all about it. Donna told me how it came about. As we lay cuddling she told me that Mac was in the sea and when he came out he hadn't realized that his cock was dangling out of the leg of his trunks. She went on to tell me that it was quite a bit longer than mine and it got her excited. Later back at the caravan she was struggling with the waste water. She didn't want to ask Bob as she didn't like him that much. Mac saw her struggling and came running to her aid. As he returned having emptied it she remembered his cock hanging from his trunks and went a little red. He noticed her flushed look and asked what the matter was. She blurted out to him that she had seen his cock dangling. He said he had hoped than nobody had noticed as he eventually discovered his wardrobe slip and rectified it. Donna blurted that it was hard to miss. One thing led to another and Donna was soon on her back discovering what a long thick cock felt like. As they were both on their own he spent the night and indeed several more. It was one morning when Bob saw Mac leave our van and go to his own. He had been wondered how come Donna hadn't needed the waste emptied or anything else done, and had been keeping a very close eye to see what was happening. Then he caught them. It was now he gave Donna the ultimatum that she sleep with him as well, or he would tell what he knew. For the last two weeks she had been seeing Mac, and then Bob would fuck her afterwards, as Mac tried to be discreet and return to his own caravan. I told Donna I had a plan that would involve Mac. When I told Donna she agreed to it straight away. That evening I lit a barbecue and put some steaks on it and some veggies. Mac looked out to see who was having a barby. When I saw him looking I invited him over telling him there was plenty to go around. Mac joined us and I threw another steak on and handed him a beer. Donna was inside doing some salad and some potatoes. As we supped our beer I told Mac that it was ok, and that I knew he was fucking my wife. For a moment I thought he was about to do a runner, but because I told him again, it was alright he settled back into his chair. It was now that I told him my plan. He sat gob smacked when I told him that after I had gone home for work he was to sleep with Donna again and in the morning make it obvious that he was going to his own van and then sneak back and catch Bob trying to force Donna to sleep with him again. Mac thought it was funny and a good idea, plus he said it was a privilege to be allowed to sleep with Donna. Mac being a big man would be able to handle himself with Bob. We hung out with Mac for the rest of the weekend. I could see Bob watching us. On Sunday night I made a thing of kissing Donna just before I got into my car and drove off site. I parked up and sneaked back to the top of the hill and watched Mac enter my van. I knew what they would be doing shortly and so did Bob as he was sat outside watching Mac sneak into my van. I then had to drive home. The next evening I rang Donna. She was with Mac and I asked how it went. True to form Mac left in the morning and when he saw the manager go back inside his van he quickly sneaked back into my van. A few minutes later Bob was at my van door. The cheeky bastard even let himself in. Mac had hid in the toilet area and listened to Donna telling him she didn't want to sleep with him. He told her that unless she wanted him to tell me on my next visit she had better get on the bed and take her clothes off ready. It was at this point that Mac sprang out of the toilet and punched the Bob the eye. Mac was lining up to punch him again as he started to get up from where he had fallen. He was far to fast for Mac and was out of the van and half way up the field to his own van. Donna said they had a good laugh, and Mac called out and a good fuck. I told them I would see them Friday evening and enjoy themselves. When I arrived Bob was nowhere to be seen and Mac was sat with Donna supping some of my beers. I shook Mac's hand and thanked him for looking after Donna. He reminded me that it was his privilege and pleasure to look after my wife. He must have felt that I wanted to be with Donna on our own and went to go. I told him to stay and handed him another beer. I suggested that I would like to see him fuck my wife. he looked a little uneasy, but I assured him it was what I wanted, and if Donna was up for it I would perhaps join in with them after watching them. When Danna came back out the van I told her what I had just put to Mac. She jumped at the idea. The started by just kissing and when Mac could see that I was ok with it he took Donna's tits out of her blouse. Then when he again saw that I was ok he stripped Donna and was licking her pussy. Then it was Donna's turn to remove Mac's clothing. What a cock, Donna was right it was big. It was probably nine inches in length and quite thick. No wonder it hung out of his trunks. Donna could barely get half of it in her mouth. What she did, she was enjoying from the Mmmmms that came from her mouth and It was very evident that Mac was enjoying it. Mac gave me another look to see that I was alright with it, before he finally plunged his cock into Donna's pussy, and then Donna was moaning her head off as he plunged slowly in and out for the best part of twenty minutes. He pulled out and came on Donna's stomach telling me that we didn't want any mistakes running around. I later learnt that all the condoms were Bobs as Mac always had trouble finding ones that fitted and due to that always went bareback. Looking at it I could see and understand why he had trouble getting condoms to fit it. As Mac rolled to one side I was on top of Donna in seconds plowing my cock in a much looser pussy than I was used to. But the excitement of what I had watched soon had me coming anyway, in Donna's pussy. Later Mac had another go with Donna before he left us to it and went to his own van. The next morning I went to empty the rubbish and there was one used condom wrapper in there. I took the condom out and put it in my pocket and then waited for Bob to leave his van. He was mowing the grass in the adjacent field when I went to their van and knocked. His wife opened the door when I knocked. I handed her the used wrapper and told her, "I believe your husband left this in my van on one of his visits." Then I returned to my van. The argument that happened when he returned from cutting the grass was unbelievable. She was hitting him and throwing his stuff around and at him, as well as telling him that it was the last time he was cheating on her. Then she want back into her van and locked the door. He was banging on the door for a while, but it was obvious there was no way she was going to let him back in. He eventually collected up his stuff and put it in his car and left the site. I think that over half the people on the site were outside their vans or tents watching the action. By far the best entertainment on the site. Later Susan came down to our van. We were sat outside and she was apologizing for her Bob. I handed her a beer and told her to sit with us a while. She didn't seem that surprise or upset to find that her husband had been cheating on her. Susan told us he had cheated many times. Donna went and got some wine from the fridge and we were soon on the wine. Susan told us that since they had been running the site he had slept with at least three other women to her knowledge this season alone, all were married and on their own as Donna was. I told her about him blackmailing Donna. She looked surprised when I told her that he had watched Mac with my wife and then pounced on her. She said it sounded typical of him and said that I should have given him two black eyes. I explained that It was Mac that had done the deed. It was at this point that Mac came and joined us and brought several bottles with him. Susan was a little tipsy by now and blurted out that was it true that Mac had a large cock. Donna answered for Mac and told her it sure was true as she undid Macs shorts and struggled to get it out of his pants. Susan just looked at it and moaned. We were still outside so Donna took Mac into our van to sort out the rapidly stiffening cock. Susan asked didn't I mind my wife with Mac and his big cock. I told her it excited me knowing she was getting well and truly fucked with it. Susan was up out of her chair and almost dragged me to her van. I spent the night fucking Susan while Donna was fucking Mac. The four of us spent the next day together and went off into Swansea for a day out. That night Mac and I shared the two women and Susan had her first taste of a big cock. The rest of the summer Mac took care of both Donna and Susan while I was at work and at weekends we shared both women. Mac took on the duties of running the site for Susan. The same arrangement lasted for another two seasons and on the start of the following season Susan announced that she was getting married to Mac, and that from now on their relationship was to be a monogamous relationship. I could see the disappointment in Donna's eyes, but we stood by their decision. At the end of the season we attended their wedding. After that it was never the same and Donna had me move our caravan to a site nearer to our home. I hoped she would find herself another Mac, but I'm not sure she ever did. If she did she never told me.