Kirk knows what he has with Spock is tentative, Spock Prime not withstanding. And despite his teasing and poking, he really, really, really wants... whatever the hell that it is he has with Spock to work. He doesn't care about destiny or whether they were great together, Jim is going with instinct. He's going with his gut which says "Keep Spock around". That's why, if Spock asked something, he will... make a concession. And sometimes, Spock rankles him because Spock is irritating and logical and DOESN'T KNOW WHEN TO DROP THE SUBJECT, Kirk is relieved to have him by his side. Bones is his personal support, but he needs Spock to lean on, to check on his decisions. Because he's still getting the hang of being a captain and he doesn't want to be a screwup anymore.

THE KISSING GUYS THING IS SO WEIRD AND NOT HIS THING. It's not even because of his sexuality or anything like that, god no. It surprised him completely and when Kirk is surprised, he gets flustered and annoyed and cranky because he wants to be in control. He gets off being in control! And he really likes girls, what if girls like him less because he was seen kissing guys ;;