Green’s Dictionary of Slang

(US) a girlfriend; used by either gender.

1925		R. Lardner ‘Zone of Quiet’ in Coll. Short Stories (1941) 65: ‘I’m off at seven o’clock,’ said Miss Lyons. ‘I’m going to a show with my G.F.’.
1932		J.L. Kuethe ‘Johns Hopkins Jargon’ in AS VII:5 332: g.f. — girl friend.
1957		K. Amis letter 2 Jan. in Leader (2000) 500: G-f may want to come when she gets wind of it.
1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 349: The term ‘B.G.’ (Best Girl), popular in the thirties, seems to have become dated, and has been replaced by ‘G.F.’ (Girl Friend).
2012		M. Lacher On the Bro’d 43: Maryann, his gf, and Carly, this new chick.