"The human race is unimportant. It is the self that must not be betrayed."
In Nicholas' intellectual domain, the reality of the situation has little bearing on his reasoning. He doesn't care so much about the theoretical value of life, finding people uninteresting and predictable. He's much more enthralled by his own experience, eager to understand his own mind. And that quest is sacred to him.
"To write poetry and to commit suicide, apparently so contradictory, had really been the same, attempts to escape."
Bored to death by his life and the perceived ignorance of his peers, Nicholas does attempt suicide, but he fails. Through the endeavor he realizes that the creative and destructive force are one and the same. While he though he was healing himself through poetry, he was merely avoiding difficult truths. He wasn't trying to make a place in this world but rather trying to leave this world behind entirely, just like his attempt.
"'Greece is like a mirror. It makes you suffer. Then you learn.'
'To live alone?'
'To live. With what you are.'"
On their trip in Greece, Alison and Nicholas struggle to relate the way they used to. Time and Conchis' experiments on Nicholas have radically altered them. While Nicholas had previously believed that Alison was the solution to all of his troubles, all of his existential boredom, he learns here that actually, no, she's not. This trip to Greece reminds him that he still has yet to face the full weight of existence. What if his internal dissatisfaction is never satisfied?
"Liking other people is an illusion we have to cherish in ourselves if we are to live in society."
As a solipsist, Nicholas must come to this realization by trial and error. He learns to pretend that he is agreeable and that others are fascinating in order to survive socially. It's a compromise he makes in order to enjoy the benefits of social acceptance.
