Author's Note: I have no idea how (if?) canon will end up resolving the whole time-traveling Steve issue, but these 300 words of alternate timeline solution is what I came up with when considering that Steve Rogers would most definitely not be happy sitting on the sidelines and that the movie made such a point of time paradoxes not existing.
Steve tried to understand Bruce's explanations about the impossibility of time paradoxes, why they were able to mess with their past without affecting their present. From the way Rhodey and Scott had reacted, this was not how time travel was supposed to work.
But whatever the reasons, knowing that nothing he did would mess with what he considered his timeline, once he'd returned that last Infinity Stone, he knocked on Peggy's door. The look on her face made it all worth it, and for the first time since the ice Steve allowed himself to close his eyes and just let go.
With this timeline's Steve Rogers still asleep in his cold bed, they didn't announce his return. He didn't have his shield anyhow, but after a wonderful few months during which they got married and took an extended honeymoon, they both decided that it was time to return to work. For Peggy, this meant SHIELD and rooting out the beginnings of HYDRA, while Steve donned a new uniform. Nomad's first mission led him to Russia, to look for Department X. For Bucky.
Because there was no way in hell Steve Rogers would stand idly by while somewhere out there, Bucky Barnes was being tortured and brainwashed, even if it wasn't technically his Bucky. Not that it mattered when the Winter Soldier looked up at him, confusion in those familiar grey eyes, and asked in a small voice, "I know you, don't I?"
"You've known me all your life, Bucky Barnes." Steve helped Bucky out of the cryo pod and into the light. He knew he'd go back to his reality eventually, close this loop, but not just yet. Not when he finally had the chance to live his life with the two people he loved the most by his side.
