@samsonjasVery different than what you perhaps have in mind, but peripherally on the theme, and "based on true story":
Couple of years after dissolution of the USSR, in one of the splinter republics... the land was still in practice lawless, economy was nonexistent and inflation was at 10,000%. We were kids of the underground national independence movement trained to be spies and pathological liars, emerging from a devastating victory in a brutal mind-war, but otherwise high school was as high school is.
So, I had a girlfriend, let's call her Jenny.
I got her at the start of what correspond to junior year in high school out of a bet with another girl that I could in fact seduce next random girl coming down the hallway. Jenny was a slightly chubby girl with big boobs, long, slightly curly brown hair, absolutely no grip on fashion and lowest observed self esteem of any girl a guy could install as school beauty queen on a whim with just some coaching and political machinations, just because the above mentioned other girl snorted that getting in the panties of that ugly grey duckling was much too easy. Well, I owned the school newspaper by then so that was in fact easy too...
Most didn't know Jenny had lost a year jumping schools, out of reasons I never truly got grip on, but might have involved a rape. Yes, she was a very broken doll, but I got my fun playing with her even if sometimes with a pang of guilt. Because yes, I had my own moral obligations to keep loyalty at least as long I found the situation mutually beneficial, but she was just rationally convenient and I wasn't really nowhere head over heels lost in love, while she had successfully deluded herself into believing she was indeed.
Okay, nothing of that is of substance to the topic, actually, but perhaps helps to grasp the environment.
Jenny still kept in touch with her bff from her old school, let's call her Evelyn.
Since, Evelyn had become, or at least claimed to be a major starlet at the center of her social bubble to the point it strained her to keep the pose. She was prim and proper stunning magazine cover round cheeked blonde, her sophisticated style aided by pocket money budget unthinkable for most, provided by her daddy, painted for me as a patriarchal asshole getting rich in the hurry by all means necessary amid the ruins. She was absolutely paranoid towards him, and I never as much as saw him in person, so can't really know.
Supposedly, it was orginally Evelyn's own project to organize a three days weekend spring rafting trip for her class. For whatever reason, there was no love lost between her and their class teacher, plus whatever quasi-political high school society 5D shenanigans she might have been in the middle of went marginally wrong maybe, and the princess had disbarred her presence from the happening in a fit.
Evelyn still wanted the experience, despite, or because, seemingly having never stepped her foot where stiletto heels wouldn't be practical footwear, so she had ostensibly assembled an alternative splinter group, but that needed a dependable and relatable outdoorsman guide, and I was invited in that category.
It wasn't at all that crazy off an idea. I had respective experience done very much the planned trip a year before with my four year older sister and cousins, and that wasn't the only time I had been on a raft in the rapids. And while sleeping in a city flat most weekday nights I insisted on calling grandfather's farmhouse my true home. There, I had been wandering around in wilderness for miles and many hours at a time since forever. According to family legend even as a little baby I would occasionally disappear, causing total panic for everyone obviously, while casually grabbing a happy nap under the jasmine bushes in the yard.
So, on my end adults were rather concerned would the other, all a year older, participants accept my authority without anyone to enforce it than about my ability to take care of myself. On that note, Evelyn introduced me with some guy, supposedly her more-or-less boyfriend, and while a jock, he seemed reasonable, and so were the other two girls present. Supposedly there was a third guy being mentioned, while unseen, everyone assured me he's cool too.
Jenny's automatic participation was an afterthought for everyone. I had taken Jenny out to the farmhouse for a weekend already, and while some formal appearances were still made, there was little doubt left were she actually slept then, and Jenny's fear her mother would find out we had sex was long ago overdue. That woman was weird in her own way, but trusted me entirely too much, and knew everything of course, but even so I couldn't get them to actually talk between them.
When we arrived at the train station in the morning, and met there only with Evelyn by herself alone, demanding a hug for a greeting from me, I almost called it off right then. Almost. Jenny didn't need to tell me anything to confirm Evelyn's claims the others would join us at the other end was just little more bullshit. I was going out for three days on the river with two girlfriends needy in totally incompatible ways. And oh boy, was I right in my immediate assumption Evelyn's true plan included her going totally off the rails on my, or rather Jenny's expense.
We started further upstream and little later than the class was scheduled to disembark their charter bus, planning to stay behind, but spot them in front sooner than would like, and overcome once they stopped for lunch the first day. While Evelyn impersonated an extra big bag, Jenny was a little worried, but chances anyone would recognize her as we drifted by were minimal, and she was effectively a stranger to her old class anyway. Not "sick at home" Evelyn supposedly was by her class teacher information, while with her class as far her parents knew.
Both girls got additional thrill out from skinny dipping, knowing at least in theory that whole class could emerge from the curl of river upstream. And it was the only time ever I have vandalized a sandstone outcrop leaving a gigantic inscription trolling people I didn't even know. But if that's an excuse to help a naked blonde to climb up a cliff in a very galant but nonetheless touchy-feely way...
Well, I should leave it there, but... I don't know what the deal between the girls was, if there was any at all, but I failed to reconcile a full threesome, and had to deal with two decidedly unhappy women more than I would have liked. It was abundantly clear this particular thing with Evelyn could only ever been an one off adventure, but nobody was helped with that realization, unfortunately.