Green’s Dictionary of Slang

1. to commit oneself.

1899		C. Rook Hooligan Nights 135: He didn’t fall that night, nor the next night.
1920		Ade Hand-made Fables 48: Joe looked to her like a Bushel of Oats until he began to pull down at the Works, when she and her Maw suddenly sat up and exchanged Glances and fell to the Fact that they were harbouring a Live One.
1929		S. Rohmer Day the World Ended 44: The gink driving the car fell for ten dollars and brought me here first!

2. to get married.

1912

T.A. Dorgan in Zwilling TAD Lex. (1993) 103: I thought I’d like to get married [...] I’ve been thinking it over and I think I’m going to fall.

3. to fall in love.

1924		P. Marks Plastic Age 148: I fell pretty hard. She was so—er, dainty.
1937		P. Cheyney Dames Don’t Care (1960) 116: Just when a dame thinks I’m fallin’ — well, I usually ain’t!
1964		B. Jackson Get Your Ass in the Water (1974) 101: She lamped my roll [saw my money], fell heart and soul, / and wanted to dance with me.