Tony doesn’t tell Steve about Captain Jack Harkness’ sexuality before they start watching. He just tells him that there’s this Science Fiction show called Torchwood, and in one episode they go back to the early 40s.
Steve sits through the whole episode with his face like stone, never turning away from the screen. Tony thinks maybe Steve is confused, or is mad at being tricked into watching military men from his time flirting.
Then, near the end of the episode, all pretext of the relationship vanishes, and the two captains slow dance together, knowing that one of them will travel far into the future and the other will never return from war.
Steve is still barely moving, eyes focus unwavering on the screen. He wipes his sweaty palms on his old-fashioned trousers and swallows hard, clenching his jaw a little tighter. But his face tells it all, eyes rimmed red and full of unshed tears.
Tony gapes, uncomprehending. It’s a miserably sad episode, yes, but it was not the reaction he expected from Captain America.
"You okay, Cap?" Tony asks, tentatively.
"Yep" Steve says softly, standing up as the credits start to roll.