I didn't know about Countdown and wish I had because it makes things clearer. Suddenly Nero is less of a one dimensional vilain and you realise that Romulus in the 24th century and Vulcan in the 23th were destroyed because neither race was willing to trust the other despite Spock's best efforts. What he must feel is beyond guilty. I wonder if it's not what makes him to appear so eager, almost desperate (as much as Spock can look desperate) to make his alternate and younger self's life better and fulfilled, because he thinks his came to a failure (he didn't succeed in convincing the Romulans and the Vulcans in time). He looks like he's ready to let himself die in that cave when nuKirk arrives and gives him purpose again. I hope he'll help the Vulcans as much as he can in the alternate time line, I wouldn't like him to end his life in misery, beating himself up for something he tried so hard to prevent but couldn't because Romullans and Vulcans had their heads up in their asses.