There are things they won't say. There are the things they can't say, the stories that must be lived and not told, that must not be hinted at beyond the mention of "Spoilers," but those stories are different from the things that they will not speak aloud, words like, "I've missed you," or "I need you," or, more important still, "I love you."
It isn't that they don't love: they do, and deeply. Beneath cool and collected exteriors beat hearts that break daily for the hurts and sorrows of other people, for loves lost and civilizations perished. But they know the power of words; they know how words can move worlds, raise armies, recreate existence. To speak love aloud, to give it voice and shape and potency, admits an unbreakable tie to another person, a person they each already know they cannot help but lose.
And so a reticence born of knowing the tangled web of their pasts and their futures keeps them silent, but silence does not win the day. They break their own unspoken rules, learning to hear what has really been said, learning to say love by hiding endearments in other words, like the promise in a simple "Hello." They cheat at their own game so often that occasionally it is hard to remember the rules, and it is of no particular surprise to either of them when they finally dispense with the charade entirely.
He says it first. With all her boldness, perhaps it should have been her, but as they sit amid the beauty of the fields of Asgard, the fading sunlight playing a warm symphony of color across her skin, he finds himself utterly transfixed by the impossibility and the magnificence of her. Before he can think to change course, he reaches out and takes her hand and says, "I love you."
"And I love you," she replies, resting her head on his shoulder. "To the ends of the universe, my love."
"I know," he says. He kisses the top of her head as the setting suns dip below orange clouds. The curls of her hair tickle his nose, and he smiles. "We've been."