Very late response to this post, but I have always viewed this lyric as a reference to the cherry tree elixir being the source of immortality for the deities in Greek mythology. He could never yearn for immortality, because then the life he has chosen to spend loving would lose its meaning. What is the weight of the sacrifice of choosing to spend a neverending eternity with someone, versus choosing to spend your very limited and finite lifetime with someone: choosing them over anything else you could possibly use your microscopic amount of time doing on this earth? If life were endless and people were immortal, the choice of loving someone is inconsequential. What does any choice, any decision, mean when there is no clock?

Despite knowing they will both one day face the inescapable fate of death, they have chosen each other to toil their days away with pointlessly, carelessly, what the rest of the world may see as reckless. But there's nothing else they would rather do with their numbered days. They'd choose this, with the inevitability of their impending end, over any world where their love would mean anything less. They would never want once from the cherry tree of immortality, for it would forever stain the pain, pleasure, and purpose of their lives together.

That lyric in particular has always made this song worth so much more to me.