They were originally related, but they had never been as dependent on each other as in those words in the book.
He always thought that all they had was each other.
In the end, it turned out that those unilateral promises were just wishful thinking on his part.
He thought he could start over again, that everything would turn around.
But that person... Doesn't need him anymore.
So what's the use of keeping these promises and this endless time?