To carry on a cause: “The columnist feels that he is carrying the torch of liberalism in an age of conservatism.”
To love in a suffering way, esp because the desired one does not reciprocate: She was carrying the torch for W C Fields
[1927+; origin unknown; said to have been coined by a Broadway nightclub singer named Tommy Lyman, when he said, ''My famous torch song, 'Come to me, my melancholy baby' ''; Venus, of course, carried a torch regularly]