The story is from the point of view of a male. He has two friends that come back from college (I think). A guy and a girl and they decide to sneak into their neighbors pool. They dare each other to undress which they do. The neighbors then come home and the main characters buddy is able to book it out of there, while the main character and the girl are stuck hiding in a small shed. They spy on the neighbors as the neighbors start having sex in the pool. The main character and the girl become aroused and as a result of their cramped, sweaty situation, they “accidentally” have sex.
The story and the relationship then develop from there.
Source: reddit.com/r/eroticliterature/comments/5clo7k/request_looking_for_a_particular_sex_story
Based on your description I went ahead and made a story about this. It ended up being too long to post as a comment (whoops), so I made a whole new post with it, but here’s a good chunk of it (you can find the full post here https://redd.it/5d751z) :
The Henderson’s kept the gate to their backyard unlocked, so it was easy getting into there. They set up the ice chest and grabbed another beer each, Scott was clearly drunk and despite Kayla telling him that he should slow down, he was still drinking. Kayla was the first one into the pool, elegantly slipping out of her dress and diving in, despite being drunk. “Well, what are you guys waiting for?” she called up to them afterwards. “I’m not feeling too great after that last beer, but Toby’s about to join!” Scott said as he pushed Toby into the pool. “Not fucking funny,” Toby yelled at him, but they were all laughing. After a few minutes they heard a car pulling up to the driveway and Toby panicked. “Shit, they must be home early, we have to get out of here now,” Toby told them. He didn’t think he and Kayla would be able to get out of the pool and their backyard in time, as Toby was thinking about what to do, Scott grabbed the ice chest and took off towards the gate. “The pool shed,” Kayla whispered to him urgently, it was close enough that they should be able to make it over there in time. They hurried out of the pool and grabbed their clothes first, then barely made it into the shed before they heard the Henderson’s laughing as they came out into the backyard.
The shed was cramped, there was barely enough room for the two of them to stand face to face. Kayla was dripping wet from the pool and only wearing her bra and panties, she didn’t have time to put her dress back on before running in here, and Toby was the same and only had a pair of shorts on. Toby had imagined moments alone with Kayla like this, though not the part about nearly being caught by his neighbors, but had never imagined it would actually happen. It was cold in the shed, especially since they were wet and hardly wearing any clothes, Toby could feel that Kayla’s nipples were hard, and were rubbing against him in the cramped room. Kayla seemed unaffected by being this close to him, though, and was more focused on the neighbors than Toby at the moment, but he couldn’t take his eyes off of her. He just hoped that she couldn’t feel his erection growing against her.
They had a small window in the door that they could see through, from there they could see that Mr. and Mrs. Henderson were stripping naked and passionately kissing. Toby finally broke his gaze from Kayla to see Mrs. Henderson’s naked body glowing in the dim lighting in the backyard, she was in her early thirties and looked good, but Toby never would have guessed that she looked this good. Mr. Henderson led her on to the ladder halfway out of the pool while he got in and started going down on her. Kayla finally seemed to realize how close she was to Toby and that their faces were only inches apart, their bodies pressed together. He could feel her breath on him, their eyes met…
“This is so fucking hot,” she whispered to him. He was surprised that she said that, expecting her to be angry with him being this close to her. “They were so close to catching us… I’m so turned on right now.” He couldn’t believe what she was saying, “You’re drunk…” he told her, “Only a little, but that doesn’t matter,” she replied. He could feel his erection getting harder, there was no way she couldn’t feel it now. She smiled at him, “Don’t worry about Scott, he won’t mind. I want you inside me…” she said before starting to kiss him. Suddenly, they could hear Mrs. Henderson moaning in pool, which only seemed to arouse Kayla more, and Toby had to admit, it was arousing him as well. Outside they could see that they were both fully in the pool now with Mr. Henderson slowly thrusting inside of his wife. Toby couldn’t take it anymore, he didn’t care about Scott right now, he just wanted Kayla now, consequences be damned.
Toby tore her bra off, this aroused her even more, she started grinding her hips against him while vigorously kissing him. He could feel the tip of his cock rubbing against her pussy. She was softly moaning now, they stopped briefly to finish stripping down. Outside, Mr. H now had Mrs. H bent over the ladder, fucking her from behind, she was moaning loader now and he was thrusting faster. As soon as they were both completely naked, Toby thrust his cock inside Kayla, she was really wet and warm, and he slid in easily. She gasped as he went in deeper, he grabbed her ass to pin her closer to him, she started nibbling on his earlobe. Toby knew he wouldn’t last long at this rate and could feel himself getting ready to cum already. Outside, they could hear Mrs. H telling her husband that she was about to cum, and to fuck her harder. Kayla was even more turned on by this, wanting Toby to finish at the same time as Mr. H. Toby thought it was a little weird, but it was arousing him as well… She started moaning for Toby to fuck her harder, just like Mrs. H was telling her husband. From what they could hear, the Henderson’s had just finished, and It didn’t take much longer for Toby to cum. She told him to cum in her, he thrust himself as deep as he could as he came, then they stayed like that for a minute afterwards…