Alone
He used to come here with Spock. But then, Kirk thinks, there isn’t a place on the damn ship that he hasn’t been to with Spock. The observation deck at least has the advantage of being completely deserted, and he makes sure to lock the door so that it will stay that way. He doesn’t want to be alone, but he wants even less to be around people. He knows his friends are trying to help, but he can’t deal with sympathy, or worse, pity, right now.
It wasn’t meant to be this way. Kirk came to terms long ago with the idea that he would die alone. He never thought that living alone would be an issue. Not since the V’Ger incident all those years ago. Spock had the advantage on almost every count; Vulcans were stronger, more resilient and longer lived than humans. Kirk's seen Spock recover from things that would have killed a human; seen him almost die at least half a dozen times. It’s hard to believe that this time it’s real.
Kirk reaches instinctively for the place of comfort in his mind. All he gets is a sensation of complete emptiness. He remembers a few times over the years when one of them was ill or injured and Spock blocked off the bond. The feeling wasn't pleasant, but it was nothing compared to this. This time their bond isn’t blocked, it’s broken. For the first time in over a decade he is alone in his mind, and he doesn’t think he can bear it.
Something inside Kirk breaks and he lets out a sob, sinking to the floor. He doesn’t know how long he sits there, letting all of the pain and anger and grief spill out. But eventually he wipes his face, and stands to look at the stars.
This isn't the first time he's lost someone he cares about. Gary, Edith, Sam.... The difference is that in all those cases Spock was there. He always knew exactly what to say or what to do; was able to comfort Kirk when no one else, even Bones, could. And now Spock's gone and Kirk doesn't know how to live without him.
“Live long and prosper,” he mutters bitterly. “How? How am I meant to do that when it feels like I’ve been ripped in half?” He takes one last look at the view, and then leaves, intending to find Bones and drink until it doesn’t hurt anymore.