There is something deeply satisfying about having Keith asleep in his arms. Curled safely into his chest where no one can touch him. During the day he has to nix the urge to pick the Red Paladin up and carry him somewhere private and defensible. Away from those who would injure him body and mind. He can't let his desire to protect something precious override his obligations to the universe. His duty requires him to order the Red Paladin into battle. Battles with lasers that burn through armor and blades that rend pale skin. They are fighting a war, and he can't spare one soldier from the front lines. Even if he must watch it crack and break small smiles, fleeting happiness ground under the horror.
That is during the day. At night, at night, he doesn't have to hold back. He can pull the smaller body down to his bed. Hold him close, and sooth as many hurts of the day as he can. Whisper softly into his ear how much he means to him. Brush the hair away from his face so he can kiss him. Sometimes they go further, enjoy each other in ways that help him remember they are both alive, but other times, like now, they simply stay close. Letting him revel in the warmth of the other body. Granting assurance that all is well in the steady puffs of breath against his bare collarbone.
He wishes he could spend forever in this moment. Someone less tired, less broken down, might wish for an end to the fighting, so they could take Keith away to his desert shack and make him happy for the rest of his days, but Shiro realized long ago he'd never see the empire defeated, so he just wishes tomorrow would never come. That Keith would sleep safely against him for eternity. No danger, no pain, just peaceful rest for all time.