Diplomatic incidents happen all the time, but not all of them end in marriage. And not all trips to alien planets involve a mysterious killer. Sam and Steve are having all kinds of new experiences lately.
Sometimes Steve and Natasha help each other out. (Pre-Cap2 porn.)
Bucky and Natasha drive around the country, taking out HYDRA agents. Along the way, Bucky learns a thing or two.
Sam thinks of that moment when he agrees to go with Steve. He always liked a challenge, and Bucky - who knows about Bucky? Sam's there for Steve, because Steve's brought him more challenges than he's experienced since he became a PJ to begin with. He goes without a second thought.
(Sam backstory with a tiny bit of kissing.)
Bucky accidentally becomes a surrogate brother to half the neighborhood, purely via the power of PBS.
Sam's had a lot of unexpected experiences and has dealt with a lot of shit. But all of that pales in comparison to what happens when he and Steve find Bucky.
(Or, Sam becomes a part-time therapist, falls in love, and gets some closure. Not necessarily in that order.)