To him, the world was separated into that which was eternal, and that which was not. Like a scientist he picked things, events, people up, and inspected them, scrutinising their meaning. He devoted himself to them, engulfed himself in them, wondered about them, despised them, despised himself, and inevitably realised that they belonged to the category of the non-eternal.
Only that which was eternal had meaning and value. That which was not might as well not have existed. Such was the standard he exacted upon the world, including himself. His quest was for eternity, and he was destined to give up all that was ephemeral but good to the crushing, relentless onward tread of time. He would not realise what he had done until he was at the brink and had reason to turn around. But when that happened he would comfort himself, that he too was paltry, just like everything else he had destroyed. Then the blink of the cosmos would complete, and he would be gone.
It is greedy, he thought. Things cannot survive being stretched so thin across time.
There was a book he had been thinking about more and more recently, one that was very important to him. It was a gift from one of his best friends (because he knew he liked the book). But he lost that friend, only the book remained. It pained him to think of the book because it reminded him of the loss, but it was a book that he related to far too much, and he could never escape.
It had seemed like the beginning of happiness, and Clarissa is still sometimes shocked, more than thirty years later, to realize that it was happiness; that the entire experience lay in a kiss and a walk, the anticipation of dinner and a book... What lives undimmed in Clarissa's mind more than three decades later is a kiss at dusk on a patch of dead grass, and a walk around a pond as mosquitoes droned in the darkening air. There is still that singular perfection, and it's perfect in part because it seemed, at the time, so clearly to promise more. Now she knows: That was the moment, right then. There has been no other.
He looked up from the web page he had googled on his phone; he had missed his stop.
Addendum
He took out the book, the gift; the cover was wrapped perfectly in plastic, so tightly it warped (he was always too much of a perfectionist for his own good), with little green tabs to mark out the pages with the parts he knew were special to him.
He sat down on his bed; he did not know what to do.