Kirk opens his mouth, waiting for the words to come. When they don't, he has little choice but to close it again. There is a heavy weight on his chest, the burden of love, which pounds and trembles within him.
Awkwardly, he settles on taking his first officer by the shoulders, feeling the tenseness in Spock's muscles relax under the pressure of one whom he knows so well.
"Farewell, Spock." He says, the words soft and fragile in the air, laden with all that could not be said. The rest he tells with his eyes.
There is a long moment before their gazes are torn away from each other. Kirk's fingertips linger just long enough to dance down Spock's arms until they tingle against the Vulcan's own sensitive hands. And then they are apart, together and separated for the last time.
"Live long and prosper." Spock says, taking an audible breath. "Jim." He had almost uttered the word "t'hy'la" instead.
Spock turns and steps onto the transporter pad, holding the image of his golden captain in his eyes until his body dissolves into energy.
Spock loves his captain more than he could ever voice aloud at the risk of losing everything. He loves him too much to stay.