its steve/bucky, set post winter soldier and ultron but pre civil war i think-tony and vision certainly help out-10-20k words, told mostly from sam wilsons POV with a little bit of steves thrown in.
here is the plot-
steve and bucky somehow get zapped to an alternate dimension with some hydra tech that wipes their minds (like bucky used to get but better somehow, more permanent) and sam and wanda and tony and i think natasha and clint try to work out how to get them back. after two weeks they get them back but its been 20 yrs in some jungle place for them. they havent aged at all, but they've mentally and emotionally bonded on a level where they think that they are one person and if they get seperated they'll die. they get kept initially in a hulk cage and Friday can translate their language, so the team realises the identity thing, and how they self soothe with cuddles and-ahem-oral sex, without realising what it is, just thinking they're scratching an itch. they've also scarred themselves to match the other, by constantly cutting and infecting the designs, steve has lines all down his arm to match bucky and bucky has the shield drawn on his back with the harness straps drawn on his chest. eventually they get to communicate with the team, and wanda and vision figure out they can fix their memories, but bucky doesnt want to, he wants to stay as one with steve, but in the end they both get fixed and stay together and love each other happy happy yay etc.
-sam is obviousy sad about his best friend, has to teach steve to brush his teeth
-when learning to comunicate steve calls himself 'steef' and bucky 'buggy'. when they get seperated one time he yells 'want buggy!'
sorry everyone for such detail, hope it is helpful and someone can tell me the author and title, there will be imaginary hugs and cupcakes in it for you if you do!!! :)