Spoilers for chapter 185-onward. Jossed by chapter, oh, I don't know, 199? Ish? But only in a couple small details.
It had taken less than two weeks after Watanuki had taken over the shop for them to discover that without him there to act as a bridge between them, conversations were stilted and awkward and almost painful. The tangible absence of Watanuki was like a gaping wound, an unforgettable reminder of why they both were unable to simply move on with their lives. The silence was the worst part; it was precisely the lack of angry shouting and eager adulation, of flailing limbs and rapturous twirling, that ached so badly, that highlighted the fact that the most vibrant person in their lives was so jarringly, unfathomably gone. Watanuki hadn't simply been another person in their group; he'd been the energy, the vitality, the passion, the emotion. He'd been everything in life that they had not allowed themselves to be, and when he was no longer there to be alive for them, it was as if the world came to a sudden stop; as if they'd completely forgotten that there was a world outside of their tiny little sphere; as if they were the only two left on whatever scraps of a world existed after Watanuki was gone.
They tried for some time to continue with their lives as though he was only gone for a little while, soon to return from yet another otherworldly adventure, something he would explain in great and dramatic detail, something they could laugh over, something they could wonder about together when it all was said and done. They swiftly learned that this time, all could not be said and done the way it once had, and there would be no together anymore. It was impossible to move on with their lives and still stay together when for one of them, the best of them, time had stopped indefinitely.
No one else seemed to remember Watanuki too clearly; teachers skimmed over his disappearance with barely a hitch in their lectures; classmates consigned the empty desk to oblivion; life moved on effortlessly. It was only Watanuki whose time had halted, and it was only they who noticed, they who remembered, they who grieved his loss as though he was dead. Worse than death was this voluntary separation, the knowledge that Watanuki had chosen his fate, had taken up his mantle of his own accord, had severed his ties without hesitation. Far worse was knowing that he was alive and relatively well and there, just there, and they could visit him if they wished, but he was still beyond their reach.
Neither of them felt comfortable around other people now, not knowing that they themselves were so fundamentally different, so irrevocably other. It had not bothered them before, when Watanuki had been their buffer against the normality, the simple humanity, of life, unveiling beauty and magic in the mundane and making the legendary and extraordinary seem matter-of-fact. They hadn't noticed that their friendship, exclusive and exciting as it was, had become a glass wall around them, that they had both been watching the world through Watanuki's eyes. All things odd and mysterious and inexplicable had been their normal, when he was there. And then he wasn't, and they were the odd ones, and where the three of them could likely have taken on the world and come through all right, only one of them could take on time, and so the two of them were left behind, lost and alone.
The passing months saw them drawing closer to one another, perhaps in an effort to shield themselves and one another from the world they no longer felt they belonged to. Perhaps they both wanted to cling to the few fragments of the past that remained, and being together was the better--the only--alternative to being alone. It could have been simply that in each other they saw the last traces of him, of what he'd brought to their lives, of what he'd taken with him when he went. It wasn't for love, of that they had absolutely no delusions--or rather, it wasn't because they were in love. They couldn't get close enough even to one another to connect that way. Instead, they both tacitly acknowledged the fact that they loved him--he who had been their center, their balance, the star at the core of their own little solar system. They loved him so deeply, so strongly, so intensely that even years after he had been taken--had walked away--from them, they could do little else but wait, in hope and in vain, until he could be theirs again. When they went to the shop to see him, they went separately; whether this was because they wanted to avoid any awkwardness with each other or because it was now the only time either of them got to be alone with him, they didn't know and didn't think about too much.
Shortly after Shizuka started college, Himawari came to live with him. Because of her condition, she had decided against continuing her education; the Doumeki family temple was virtually the only place she could go without endangering anyone, so she spent most of her time there and occupied her days with helping Shizuka perform temple-cleaning duties. She got along well with his mother and was delighted to discover that Doumeki-san didn't suffer in the least from being around her. So often was she a guest at the temple, Shizuka finally offered her a room and a job as caretaker of the grounds; he was in school so much and his mother had some health issues, so that they didn't have time for temple upkeep anymore. It was easier for him to concentrate on his studies knowing Himawari had a safe place to stay and people with whom she could interact without fear of repercussions.
Their bond grew deeper even if their relationship stayed the same. On some days, the two of them had entire conversations in which neither of them mentioned or thought about Watanuki at all. The memories were still bittersweet, though, and still raw, and on the days when they became overwhelming, Shizuka took his bow out of the closet and went outside to practice his archery so he wouldn't have to think and Himawari would do something like make croquettes or hold Tanpopo against her heart and try not to cry.
They decided to get married a year later. Shizuka was the one who told Watanuki. He would never forget the day, but he would never tell Himawari how Watanuki, indolent and languid, had watched him with those unnerving bi-colored eyes, how the smoke had wound snake-like and silent through the room, how he had rearranged those long, pale-as-glass limbs under the layers of rustling silk, how his lips had curved only slightly into something that was not a smile, not even close.
"Is that so?" he said, and his eyes fluttered closed for a brief moment. "Congratulations." They opened again, blue-and-gold so dark that they were almost unrecognizable. "Or are you here to ask my blessing?"
"Would you give it if I did?" Shizuka asked.
"Hmm," said Watanuki, his gaze unwavering, his not-smile gone. "I wonder."
Silence grew between them. Shizuka didn't look away from the figure on the chaise longue. Watanuki inhaled from the pipe and released a stream of smoke. His eyes were thoughtful, distant.
"You hardly need it," he said finally. "My blessing, that is. Your life is your own. Himawari-chan's life is her own as well. Whatever you two decide for yourselves, I cannot interfere. Whether I approve of your union or not doesn't matter."
"Doesn't it," said Shizuka, and it was not a question.
Watanuki's smile was an elusive thing--barely there long enough to register, then gone as if it had never been.
"I always thought you two looked good together," he murmured. "It used to infuriate me. I could picture it in my head--how you'd make the perfect couple."
He exhaled smoke again, shrouding himself from view for the briefest moment.
"Must be fate," he said.
They are getting married tomorrow. They are not the perfect couple. They're not even in love. Both their hearts belong to the same person--the same untouchable, unattainable person who stole their hearts and then broke them years ago. Time has not stopped for them. The world has kept spinning slowly in circles. Life has continued in the same fashion. The memories are still strong and the pain is still sharp. They are not in love, but they are all that was left when they were both left behind, and that will have to be enough to get them through the rest of it.