Green’s Dictionary of Slang

1. (US campus) a boy- or girlfriend.

1896		W.C. Gore Student Sl. in Cohen (1997) 17: gum drop n. Sweetheart.
1901		W. Irwin Love Sonnets of a Hoodlum XVI n.p.: Gum Drop: Your tanglefoot has got my game, I’m stuck so tight you cannot shake your catch [...] So wont you join me in a tie-up match?

2. (US Und.) a person, esp. one to be duped.

1891

A. Day Mysterious Beggar 268: I followed th’ old gum-drop, and found out who he was: ’n I took his number.