Throuple plus one

[LupusDei]

As title says... a (seemingly?) stable throuple meet someone new and exciting, much drama and sex in various combinations ensures until an obvious but unpredictable resolution is found

...with can be a full on quad, or partial breakup into two couples or a couple and two lose friends or whatever...

 

[LupusDei]

Obviously, a guy with two girls meeting a third is a harem trope a bit out of scope here. Rather, it could be one of girls pulling in another guy... but that has potential sensitivities...

What I actually had in mind is a girl with two guys meeting a girl...

 

[LupusDei]

Nina, a creative professional with charm and ambition, but also reservations caused by upbringing... she values her independence above much else.

Markus, he's older by almost a decade, when they first met he was her history teacher... obviously, nothing inappropriate went on back then, and while he moved on from that job and they met again in different setting, that still colored their renewed relationship at least early on. He's now busy with various NGOs and volunteer projects and barely getting by.

Karl, a promising startup entrepreneur a year or two younger than her, moving fast with investor money met Nina in a presentation and things developed fast, but Nina never gave up Markus and Karl had to accept that - truth to be told he's currently not got time for proper family life anyway. Guys eventually became friends, even though not for both being Nina's lovers might not have much in common.

Each of three has their own place or two (in Karl's case), and while they don't fully cohabitate at least Nina may wake up in any of those, and either of the guys or both may stay at hers at anytime, or at Karl's, but perhaps less likely at Markus lair, just for being a little too cramped for three, really.

Celine, a damsel in distress the trio "rescued" on one of the infrequent outings they're were all three together is youngest, exceedingly pretty, laud, shameless and a little disorganized, and while seemingly naive not at all that helpless as it may seem at first. An exchange student just moved into the area? Perhaps.

It just so happens each of the trio finds their own unique way to help the girl and somehow that swiftly turns... at least a little bit... "inappropriate" in each case.

 

[Rob_Royale]

I have an idea that I've been kicking around in this vein.
Two women the MMC knows at work are best pals and its common knowledge. What isn't is that they live together with a man in a poly situation. The MMC is going through a rough breakup and one night the pair take him out for karaoke and drinks to perk him up and that night they take him home, introduce him briefly to the man and then a threesome ensues.
Due to the breakup he's basically homeless, living in an extended stay and the next morning the ladies suggest he moves in with them. One man and one woman are married, and the second woman has her own room. She'd love for the MMC to fill the other side of her bed so that things feel a bit more equitable. A lot of swapping and group sex follows.