carry a torch

Etymology
From the of a burning flame, to keep a fire burning.

The association of a torch with love may date to the Greek and Roman tradition of a wedding torch, lit in the bride’s hearth on her wedding night, then used to light the hearth in her new home. Such a torch is associated with the Greek god of marriage.

Verb

 * 1)  To love or to be romantically infatuated with, especially when such feelings are not reciprocated.

Usage notes

 * Often used to characterize a situation in which a romantic relationship has ended, but where one partner still loves the other.
 * Considered by some to be dated, but still in wide usage.