Certain events come to pass and Bucky moves into the tower, but for some reasons everyone comes to the conclusion that Winter wants to kill Tony, so he is told to stay away. Tony agrees, because it appears as though Bucky/Winter has forgot about him.
Then while on a mission Tony is either injured or missing and Winter takes over in order to find him, because he claims that he will always be able to find Tony. Its during this that Bucky remembers having met Tony before and after the mission the story of how they met is shared with the rest of the Avengers.
I could have some facts wrong, but that is most of what I remember.
Any ideas? Please help!