Old Flame Meaning
(idiomatic) A previous girlfriend or boyfriend; a former romantic partner, especially one for whom one still has romantic feelings.
Example: 1839, Charles Dickens, Nicholas Nickleby, ch. 1:
There once lived, in a sequestered part of the county of Devonshire, one Mr Godfrey Nickleby: a worthy gentleman, who, taking it into his head rather late in life that he must get married, and not being young enough or rich enough to aspire to the hand of a lady of fortune, had wedded an old flame out of mere attachment.
1922, F. Scott Fitzgerald, "May Day" in Tales of the Jazz Age:
"Edith Bradin's coming," said some one to Gordon. "Didn't she used to be an old flame of yours? Aren't you both from Harrisburg?"
2008, Lev Grossman, "Text and the City," Time, 25 Sept.:
But Philip still yearns for an old flame: Schiffer, an Oscar-winning actress.