How is “fall in” used?

In Guess Who's Coming to Dinner (1967), one line is: “I fell in love with him in 20 minutes!”

Which movie is “fall in” from?

The clip at the top of this page is from Guess Who's Coming to Dinner (1967).

I fell in love with him in 20 minutes!

8 作品で登場 · 1 本目

to begin to love someone romantically; if soldiers fall in, they form lines; to drop down into a hole, crater, or other opening

146 本の映画に登場

定義：Oxford Advanced Learner's Dictionary 第 9 版