Wow so long since I've posted! Well, I saw the Winter Soldier. Twice. I have lots of feels. Don't look at me I AM ASHAMED.
I don't own Marvel, or these characters. Promise.
It had all happened quite accidentally. They didn't even really think of their relationship as polyamourous; they knew it was unusual, sure but they were two super-enhanced humans and a dude who flew so. Unusual was pretty much accepted as the norm.
Steve and Bucky had always been...close. True, there hadn't been any sex or exuberant making out, but life isn't always like a vintage gay porn. Then there was Sam. If Steve was being completely honest, he might have tried some of Natasha's flirting techniques on him. There was just something about Sam, a kind of magnetism and gentle braveness. Sam, for his part, was totally crushing on Steve as well.
This all became very obvious when they were searching for Bucky. Sam understood a lot of what the super-soldier was going through. Not the frozen for 70 years part, but as it turned out they had a lot in common. Sam continued to give Steve his "music education".
"Thank god you have me to show you the good stuff." he said with a wink one night. They were camped out in an old Romanian building, Steve leaning over Sam's shoulder and sharing the earbuds. Their faces were so close, how could our super-soldier resist dipping down for a kiss?
When they found Bucky, you would expect things to get complicated. And they did, but not in the love-triangle way we've come to anticipate. Being brain-washed to do horrible things really screw people up, as it turns out. Luckily, a certain man with wings had some experience helping people who were messed up. Sam and Steve at this point had started sharing a bed, and they didn't stop once they found Bucky. Eventually, he just sort of moved over to them, and it felt natural. After that, it was acknowledged that they-all three of them-were together in a sense. Sure, they had their fights, but no one could deny that they fit.
And that, my friends, is one of the best things of all.