Carry a torch for someone
The metaphorical connection between the flames of a fire or torch and love, have long been established. In Hamlet Act IV, Scene VII, Shakespeare uses the phrase “flame of love”. Sheridan in the epilogue of The Rivals (1775) and then later, William Blake, both use the expression “torch of love”. Then the 1920s and 30s were famous for their so-called torch songs (all sung by female artists), about unrequited love for which torches were still being carried. Perhaps the association goes back even further because, down the ages, many statues and paintings of Venus, the goddess of love, depict her carrying a torch. The advent of electric torches seems to have done nothing for the metaphor.