What, Iwanako? The fact that he wasn't happy with the letter she sent and that makes him immature? I'd feel the same way he does, most likely. Seems to me everyone can accept you at your best, but they abandon you when you're at your worst. That is how fickle human minds are... but the reason the story went that way is so we'd have a lot more than just three endings.
I honestly don't know how I would have reacted 11 years ago, because back then I had a lot more to learn than I do now.
Then again, now that my half asleep mind is just waking up, I'd think that the hospital stay pretty much would have spelled it out for me.
And if you think about it, "Me-Hisao" would have handled things differently before the heart attack even came. Like writing letters to Iwanako instead of just staring and listening in admiration. I did a lot of writing in high school. I regret not keeping it going, but I got interested in other things that helped me grow as well.
I have to keep falling back on and saying this, but were I involved in the KS story as the main character or another male, things would have gone way different cause I'd make different choices. It would be interesting to see the characters' reactions to me vs. how they deal with Hisao. It also takes a lot of what-ifs, like considering if it's my high school self or the way I am now.