"He's my friend..."

In the end, it's not even a decision- Steve knows it will always be Bucky.

Tony is his friend, but Bucky fell off a train because Steve didn't catch him. Bucky spent 70+ years as the Winter Soldier because of him. Steve dragged Bucky into fights and arguments and Bucky always dragged him home after. He stayed up 48 hours trembling as he worked triple shifts at the docks to get him medicine. Their calloused fingers mingled atop the thin tatty duvet and they had to huddle so close together for warmth that they breathed each other.

"So was I..."

Tony is a good man, a good friend. But he wasn't Bucky patching him up like a rag doll, making the best Christmas they could out of the Depression; sneaking in to see the Wizard of Oz for a third time because Steve was so entranced by it all. When Erskine and blood threw them into tiny freezing tents and desperate, heated kisses- Bucky was his everything.

The sad little look he tried to hide whenever Peggy came around. The teasing of their fellow soldiers.

And Steve knows he isn't really Bucky anymore, hasn't been for a long time. But he's his Bucky and that translates to something more than just a friend, even is his words are too clunky and old to articulate precisely what.

So he doesn't even choose Bucky. It's SteveandBucky with some guilt and cold nostalgia thrown in.