Synopsis

A merchant stumbles on a grotto when he is lost and eats his last apple. He plants the seeds the next day to provide food for future lost travelers. And so, the nymph Theanore is born.
She would grow from a tiny seed to a splendid apple tree. She would meet many friends. She will try her hand at being a merchant like her father. And she will get to know her lifetime companion, the merman Marinus.
But as every farmer can tell you, apple trees live only for about 150 years and so, with her tree dried up so will Theanore die. But before that, she will live.
I'm also posting this on Royal Road and AO3