Their bond went deeper than that and carried from The Avengers to Winter Soldier, Age of Ultron, Captain America: Civil War, Avengers: Infinity War, and Avengers: Endgame.
Not that Nat and Steve only showed chemistry in The Winter Soldier.
I wish Steve had been given more time to mourn his friend Nat in Endgame, but her sacrifice was too closely followed by Tony Stark/Iron Man’s death.
That’s one regret the Endgame writers shared about Black Widow’s storyline, that the movie had to go on instead of spending time grieving Natasha.