bucky, steve, nat, and sam all take turns proposing to each other. it starts as a game, as most things do between the four of them in their relationship - bucky goes down on one knee and pops the question to sam with a ring pop, grinning like he always does when he’s being an asshole, but then he starts crying when sam says yes, and things get serious pretty fast after that.
natasha, bitter she didn’t get to sam first, kicks bucky’s ass in the sparring room and proposes to him when she’s got him pinned beneath her. bucky, eyes wide, says yes with a breathless voice that he stubbornly maintains is from the sparring, not his feelings. nat knows the truth. she is Pleased.
steve proposes to sam in the middle of a battle. “marry me!” he calls out, throwing his shield over sam’s head. “what, right now?” sam yells over the gunfire. steve just grins at him, bloodstained and a little wild-eyed, and sam wraps them both in his wings so he can kiss him without getting shot in the process.
steve asks nat to pass him the salt over the dinner table, and she says “only if you’ll marry me.” steve says he will, so nat hands him the salt with a smirk. their ankles are hooked together under the table.
sam proposes to nat when he’s got the flu. steve’s making him soup, bucky’s down the street picking him up some medicine from walgreens, and nat’s sitting with him while she’s checking him for fever. “what’ll make you feel better?” she asks him, squeezing his hand. “marry me?” sam asks, pathetically, around his thermometer. nat just laughs and says yes, on the condition that she doesn’t have to kiss him until he’s better.
steve is sort of flustered when he offers his dog tags to bucky, tips of his ears going pink, and they both blubber a little when bucky puts them on - bucky manages to choke out “marry me? please”, and steve’s tearful “of course” is mostly unintelligible because he kisses bucky in the middle of saying it.
they all wear matching wedding bands and love to mess with people they meet who try to figure out who exactly is married to who. legally, of course, they can’t make it official, but the vows they’ve made are just as binding as they would be with piece of paper to prove it.
sam sarcastically calls bucky “babe” once - “thanks for finishing off the coffee pot, babe, wasn’t like i wanted any more” - but sam’s fond exasperation melts into thin air when he sees that bucky has blushed all the way to his hairline and is trying to hide his flustered smile behind his coffee cup