Sometimes, he stands under the tree and waits for him. [About Reminiscence, ep. 24, season one]
He knows the boy isn't coming back, knows that the boy wasn't even really a boy, was more a spirit than anything. But Watanuki likes to stand under that cherry tree and wait, because there's something in the back of his mind that says that the boy will come back. He knows that it's silly to stand there, and wait, and wish, but he does anyway.
He stands just under the branches where they used to sit most days, but on the days that he thinks that he's fragile enough to break - the days that come more and more often for him - he climbs the tree and sits in the branches, hidden from the world (like he's supposed to be).
He knows that he needs ‘help’, he knows that the thoughts that run through his mind aren't good; but he doesn't want 'help'. And he's always been critical of himself, right?
So when 'Watanuki, that was stupid' became 'Watanuki, you're stupid', he didn't see the difference.
He misses the boy that could see the strange things too, and sometimes it's so bad that there's a hollow feeling in his chest that he thinks just might break him. But it doesn't; it never does. He just slides out of the tree when the sun sets and the air is icy, and walks home with that gaping hole in his chest, and tries to tell himself that the ache isn't there.
He begins to hate his birthday, because it's the anniversary of the day the boy left. (He can't bring himself to say his name, not anymore. Not ever.) He hates his birthday, and when it comes again, he hides up in the trees and wishes everyone and everything would leave him alone.
But no matter what, he brings the salt with him. No matter what, he tried to stay safe, even if it's only because it reminds him of the boy.
"Don't be silly," Yuko likes to tell him, and even though he knows she's not talking about his visits to the cherry blossoms, it still feels that way. It's stupid of him to think like that, but he does, he does, and it feels like there's nothing he can do to stop it.
And then he starts to heal.
It's slow, and he doesn't notice it, at first. And when he does, he panics: the dark thoughts in his head are all he has left of the boy; if he lets those go, the boy goes too, and Watanuki has nothing else to remember him by, nothing but his pathetic handful of salt. But that, too, soon slips through his fingers, and then Watanuki has nothing.
... and then, Watanuki moves on.
He moves on. On to hating [sort of] Domeki, on to loving Himawari, on to sort of liking working for Yuko [no!] on to life and happiness where he can get it. And the dark thought still linger in his head sometimes, at night and when he's just done something horribly idiotic, but for the most part, he's Watanuki again, Watanuki with salt that slips though his fingers.