There's this one scene where, in the middle of a battle, Tony saves Bucky from an explosion and they end up in a collapsing building together. Knowing that there isn't enough time to get them both out of there, Tony chooses to use the last of the power in his suit to propel Bucky out of the building. Tony says something like "take care of him" and saves Bucky. The last thing Tony sees before the building collapses is Bucky's horrified face.
Thank you in advance to anyone who can help me find this fic!