In ST09 Spock Prime told Spock about the potential future he could have with Kirk. He told Spock they needed each other. He told him about not depriving him of the revelation of what Kirk and Spock could accomplish together, and the friendship that would define them both in ways he can't yet realize. You think Spock forgot that? You think after one year together he didn't see that it could all come true in the fullness of time? So, there's Kirk lying before him dead, only one year into that relationship that was meant for great things. Spock not only lost his past (Vulcan), he's now lost his future. What's he supposed to do, just mutter, "Well, crap. This sucks," and move on?