Steve knew the exact coordinates for entering Wakanda so I’m thinking he’s been taking the quinjet into Wakanda, and so really my reasoning is that Steve and Bucky have a subterranean affair going on much like Wanda and Vision, but of course we don’t see it on screen because whatever.
Also, it’s interesting that T’Challa lists all the resources that he’s made available for the upcoming fight but then ends his list with a gesture and Bucky enters as Steve practically sprints over to hug Bucky while T’Challa, Nat, and Sam look on kind of indulgently.
I’m just saying my favorite husbands in love have been canoodling under the pleasant skies of Wakanda, herding sheep and goats, living in their hut for stolen moments much like Wanda and Vision.
And you really can’t take that away from me because it’s a beautiful film in my head. Also, here’s a gif of Steve and Bucky running through a rainbow.