What He Doesn't Know

Part 1

It was the middle of the night when you got the call. Your phone buzzed and you felt around for it in the dark until you found the little rectangle with Steve Rogers' face flashing on the front. At first, you didn't think much of it since he rarely slept and for good reason so he often called you in the middle of the night.
"What's up, Cap?" You answered in a bleary voice.
"Y/N, we need you to come in immediately," Steve sounded frazzled which was quite uncharacteristic of him, "we're at the top level of the Avengers Tower in Tony's lab."
He hung up without another word and left you worried for what you would find when you got there. You hastily threw on the first pair of jeans and a t shirt you could find and shoved your feet into some sandals before you took off. If it weren't for your time manipulation powers it would've taken you at least an hour to get there, but thanks to your ability to slow down the world around you, you were there by the time Steve hung up the phone.
"Hey, Steve, what's going-" Before you got your question out you laid your eyes on the man you lost over 50 years ago. The other Avengers disappeared because you could only see one thing. James Buchanan Barnes, or at least a ghost of him, was standing five feet in front of you. He looked like he hadn't seen daylight in years and didn't know what a good meal was, but he was alive.
"Bucky came back." Was all Steve could get out.
"Oh my god, Bucky, it really is you!" You ran to your long lost friend and threw your arms around him. He instantly tensed and hesitated to return the hug if you could even call him awkwardly patting your back a hug. You heard rumors that the Winter Solider was compromised, but you never expected to see the man you lost so long ago.
"Everyone keeps calling me Bucky," he said, hopelessly confused, "that was my name, right?"
"We need your help," you had forgotten Tony was even there when he spoke up, "I can repair some of the neurological damage, but I can't reverse any of the side effects."
"What does that have to do with me?" You asked.
"We need your particular set of skills to show him who he was before he was experimented on by Hyrda." Tony never liked to admit he was limited in his line of work so you knew this was serious.
"There's only so much I'll be able to do since I can only take him back to my memories with him, but I'll do my best." You took Bucky into a small room with a two way mirror so they could observe you in case it went poorly.
"Where are we going?" He asked in a weary tone.
"It's more like when," you said as you led him to the center of the room, "I can travel through time but the farther back I go, the more limited time I have to stay there." He looked unsure, but didn't fight you on it. "Ok, Buck, so I'm going to tap into your mind and take you back to one of the memories I have with you. I've never gone this far back before so just don't panic and stick with me, okay?"
"How far back are we going?"
"About 70 years into the past."
Everything blurred together as you traveled back to 1942, more specifically the night of your first date with Bucky. The two of you were walking down the streets of Brooklyn on a cool autumn evening. He was dressed in his finest uniform, trying to impress you no doubt, and you were dolled up in a sea foam green dress with his jacket around your soldiers. It was so long ago, but watching the two of you from afar made it feel like it was just yesterday.
"That was us, 74 years ago," you said wistfully, "you asked me to go with you to the movies and I got cold on the way there so you gave me your jacket. You were such a gentleman." Your past selves were moving down the streets and you followed them at a safe distance.
"If this was so long ago then how come you're still alive, it doesn't look like you've aged a day since then?" You were hoping you could avoid that question for as long as possible.
"They selected some nurses from the front lines because they had an injection that would help us be everywhere at all times." He stopped and looked at you for second, like he was trying to form the right words before he spoke.
"I told you not to, didn't I?" You nodded, hoping he wouldn't get upset like he did when he found out, "I said I didn't want you to end up like Steve."
"I can take you to that memory," you offered, "our time is almost up here anyways, I can feel it."
This time you transported yourselves to an army base in Germany. People and soldiers were walking around distributing goods where they needed to go and running orders here and there. You led him to the infirmary tent where the netted windows gave you a view of the inside. Bucky's past self was looking for you and he asked around to see where you had gone off to.
"Is Y/N in there?" He asked a nurse that was on her way out who nodded her assent. Bucky burst through the doors as you finished treating one soldier so you could move on to the next. The look on your face spelled out "I'm not in the mood for this" as he approached you all in a huff. You were gathering bandages for a burn victim when he stomped over to you.
"Y/N!" He shouted your name, startling some of the other nurses, "What's this I hear about you signing up to be someone's guinea pig?"
"It's just a trial for some new stuff to help the nurses in the field." You said offhandedly trying not to look him in the eye and make it seem much more mild than it actually was.
"That's not what I heard about those insane scientists."
"Bucky, I'm just trying to end this war and if this will get us closer to that then I'll do it."
"No because if this is what it costs to end the war then I'll fight everyday for the rest of my life if I have to." He grabbed your wrist and made you drop your gauze so you had to look at him.
"Bucky, I-"
"It's time to head out, Sergeant Barnes." You were cut off by one of the Howling Comandos calling his name.
"I'll be there in a minute."
"Captain Rogers needs you there immediately."
"I said I'll be right there," He shouted with a hint of agitation in his voice, "And we are going to talk about this later." He planted a hasty kiss on your forehead before running out the door.
"I didn't see you after that," you brought Bucky out of his stupor from watching your past selves, "that's when Steve watched you fall from the train. We were never able to recover your body and we thought you were dead. Do you remember anything yet?"
"Some things are coming back and I remember falling off a cliff, but why didn't you listen to me?"
"What?"
"You went and did the experiment even though I didn't want you to?"
"Well I didn't want anyone else to die like you did if I could help it. That's why I haven't aged, the injection gave me the ability to slow down time and revisit old memories, but it also slows down the aging of my cells so I'll never grow old." The world started to flicker and you knew what that meant, "We have to go, I'm starting to fade."
"What happens if we stay too long?"
"I don't know and I'm not ready to find out."
The barren room came back into view as your time traveling stint ended. Everyone watched with baited breath as the two of you came back to yourselves. You felt faint considering you never travelled back that far especially with another person. Bucky held you upright as more memories came back to him.
"We can do this again later, but for now I think I'm done for the day." You said as Bucky walked you out of the room.
"I'd like that." You didn't want to show him just how close you had gotten before he went missing. There was one moment in particular that you wanted to take him back to, but thought better of it. After all, reliving the moment you asked the woman you forgot entirely to marry you would be quite a shock for anyone. You figured what he didn't know wouldn't hurt him.