Full warning: This one-shot deals with serious stuff like self hate and depression. Please don't read if it might negatively affect you!
Steve hates himself. He doesn't tell people that, of course. Doesn't tell people that is the reason why he is always in his Manifested form. Because that would inevitably lead to a discussion about Bucky. He hates his Manifested form, which of course means it will never go away because it was self hatred that manifested it. Steve hates how utterly perfect it is; he is big and strong and healthy and attractive and everything anyone could ever want. Everything he'd wanted all his life.
Until he got it.
Because Bucky had never seen his Manifested body. Had never touched it. Had never smiled at it or poked fun or wiped away sauce from his mouth or any of the little things things he had experienced in his normal form. Steve had Manifested too late to save his friend by mere hours, and no matter how many policemen had told him otherwise he knew Bucky's disappearance was his fault. And so he hates himself and is forever stuck in his despicably perfect Manifested form because he hates it too.
But his Manifested form is very powerful and he doesn't care if he lives or dies so he spends his time doing what should be suicide missions to save others. Whatever SHIELD requires. He's rescued impossible prisoners, taken down high risk terrorists, infiltrated dirty companies; once he'd even walked right into a meeting of top HYDRA personal and shot the region's leader in the face. None of it made him hate himself any less, but at least it eased the gaping black hole in his chest that had sucked in all the rest of Steve's life. The one titled 'I'm the reason my best friend went missing'.
Sam doesn't know, but he is nice enough to let Steve crash on his couch after a mission when he doesn't feel like going to the Tower. Natasha doesn't know, but she's kind enough to bring him food and water when he forgets to eat. Tony doesn't know, but he still takes the time to drag Steve down to his lab and crank up the music or talk until Steve doesn't feel so cold inside. Clint doesn't know, but he's never told anyone about the three times he caught Steve on the edge of the roof late at night contemplating stepping off (and silently kept him company until he stepped back). Wanda doesn't know, but she always puts English subtitles on her Sokovian films when she finds him listless on the couch.
It's pretty likely they know there's something. But they don't know the truth. That Steve deserves to feel this way. He'd been the idiot. He'd been rash and inconsiderate and a fool. And he was the reason Bucky was gone. Brilliant Bucky Barnes whose incredible Manifestation had given him the unbelievably rare ability to command others to do anything, but despite Manifesting so very young he had never used it for his personal gain. Never took away someone's free will, unless they were going to hurt themselves or others. Never made things easier for himself or took advantage, despite how many people had tried to take advantage of him.
And Steve was one of them.
He'd taken advantage of Bucky more than anyone. Always knew that Bucky have his back, no matter how dangerous the situation was that Steve got himself into. Relied on Bucky for everything from food and a roof to his medicine and emotional support when his mom passed away. And then he'd asked Bucky to use his Manifestation to help an un-Manifested Steve get into the army when they wouldn't take him.
It was the only time Bucky had ever shouted at him. Usually Bucky's anger was icy, contained in sharp glares and cold expressions and ruthless action. It wasn't until about a week after that Steve realized the truth; Bucky hadn't shouted because he was angry. He'd shouted because he was afraid; he was trying to protect Steve from himself like always, but this time Steve hadn't noticed or cared. Just screamed back, demanding more than anyone had the right to of his friend. Bucky had stopped talking and left abruptly after that, without his phone or wallet or jacket. He'd barely paused long enough to shove shoes on his feet.
Steve had been fuming for hours, unable to sleep because of it. It wasn't until the sun had started to rise that Steve even recognized something was wrong with the fact that Bucky hadn't come back. He called everyone, even the people on Bucky's phone Steve didn't know. No one had heard from or seen him and the police hunt that began a day later had turned up nothing more than one security video of Bucky sitting on a curb on an empty street, head in his hands. Steve didn't even need years of familiarity to see how tortured Bucky was in that video. He was there for about a half hour, had barely even shifted the whole time, then the camera had cut out for just four minutes. Four measly minutes. Just long enough for Bucky to be abducted.
Steve watched it whenever the hole in his heart started to feel a little too good. Because he didn't deserve to feel whole again, not after what he'd done. And no matter how powerful his Manifested body was he couldn't find Bucky without any leads or direction. It was a cold case, just like the hole in his chest. And Steve wanted it that way.