The number of people that Kirk trusts he can count on a single hand without using all of his fingers. He’s spent his entire life both separated from and desperately attached to the people around him, unwilling to get actually attached because he knows what is coming. Kirk can chant I don’t believe in no-win scenarios until he is out of breath, but the truth is that death has been glorified for him ever since his birth. It isn’t just a possibility, it is an inevitability; it is what good captains do.
He doesn’t fear it. He has literally nothing to lose.
He is so lonely it’s physically painful sometimes.
Sometimes he crashes out in Bones’s room because he can’t stand it anymore and it’s better than nothing. Bones has his own life and career and has a daughter and Kirk is just a needy kid with daddy issues and he feels guilty sometimes about just how much he needs. What he gets isn’t enough but he can’t ask for more, partly because he doesn’t entirely know what that more is, and partly because he understands on some subconscious level that Bones can’t provide it.
He can take rejection from almost everyone, but not the couple of people he can count on his hand.
He does his best to make it up to Bones because the friendship is so imbalanced. He doesn’t understand what Bones gets out of it and is terrified to ask, in case it reminds him that it is imbalanced and he leaves like he should, like he ought to, because he can get a better gig without an insecure commanding officer literally anywhere.
He is completely loyal to him, he loves him absolutely, because Bones has never compared him to his father, never asked about his family, never said he could do better. No one else had ever looked at him when he was at his worst and hadn’t been disappointed by what he found.
So he feels guilty that isn’t enough, sometimes, because he knows that’s more than he could hope for and definitely more than he deserves, but some nights he watches Uhura disappear into Spock’s room and he adjusts course from where he’d been headed and goes to Bones’s door instead, and he lets himself in like he always does, because he wants whatever that is so badly it hurts and knows that like Bones, Spock deserves better.