All I know is Tony went to find Bucky for Steve and he was like down in this cavern/trench/someplace that Tony had to go way far down. I'm pretty sure it was in the same spot where he fell off the train. I think Spiderman helped at some point.
It is possible that Tony and Steve had been dating or dated previously but I'm pretty sure Tony wanted to find Bucky to make Steve happy. Also I'm pretty sure there was some kind of danger around the rescue. Like Tony knowing it was possibly a trap but doing it anyway.
Sorry for the vagueness but I hope someone recognizes this a little.