Boy Meets Girl is a play by Bella Spewak (1899-1990) and Samuel Spewak (1899-1971) that opened on Broadway on November 27, 1935. One character said:
 
“BENSON. (indignantly) You couldn’t follow it? Listen, I’ve been writing stories for eleven years. Boy meets girl. Boy loses girl. Boy gets girl.”
 
The play’s formula quickly became well known on Broadway and in Hollywood. Another romantic comedy-writing rule is that the lovers must “meet cute.”
 
 
Wikipedia: Samuel and Bella Spewack
Samuel (September 16, 1899 - October 14, 1971) and Bella Spewack (March 25, 1899 - April 27, 1990) were a husband-and-wife writing team.
 
Internet Broadway Database
Boy Meets Girl
Cort Theatre , (11/27/1935 - circa. 7/1937) 
Opening Date: Nov 27, 1935  
Closing Date: Jul 1937 Total Performances: 669
Category: Play, Comedy, Original, Broadway
Description: A comedy in three acts
Setting: Mr. Friday’s Office, The Royal Studios in Hollywood; the screen of Your Neighborhood Theatre’ a hospital corridor; a Station KNX Radio Broadcast
Produced by George Abbott
Written by Bella Spewack and Sam Spewack
 
5 December 1935, Burlington Daily Times-News, “Washington And Hollywood Lampooned On Broadway” by NEA Service, pg. 3, col. 5:
“BOY MEETS GIRL” is another play (or, rather, about a twelve-penny nail) stuck into Hollywood’s inflated ego. Written by Bella and Samuel Spewak and expertly directed by George Abbott, “Boy Meets Girl” has to do with the hilariously crazy swath cut through the film colony by two irreverent scenario writers (NOT Ben Hecht and Charles MacArthur, oh, no!) who mould the new-born infant of a husbandless studio waitress into a child star, lampoon self-important studio executives, blast the career of a cowboy star and perpetrate movie plots for which the formula invariably is “Boy meets girl, boy loses girl,” etc.
 
Google Books
Boy Meets Girl; Spring Song
By Bella Cohen Spewack and Samuel Spewack
New York, NY: Random House
1936
Pg. 14:
BENSON. (indignantly) You couldn’t follow it? Listen, I’ve been writing stories for eleven years. Boy meets girl. Boy loses girl. Boy gets girl.
 
Google Books
How to Write for a Living
By Trentwell Mason White
New York, NY: Reynal & Hitchcock
1937
Pg. 100:
THE LOVE STORY ACCORDING to Boy Meets Girl, the Spewacks’ successful Broadway burlesque of Hollywood manners and matters, builders of cinema tales are agreed that the formula of the love story is, in simple: “Boy meets Girl; Boy wants Girl; Boy loses Girl; Boy gets Girl.
 
Google Books
Playwrighting for Broadway
By Leo Shull
New York, NY: The Author
1945
Pg. 34:
In the first act have the boy find the girl. In the second act have the boy lose the girl. In the third act have him get the girl.” (That famous saying: “boy meets girl, boy loses girl, boy gets girl.”)
   
Google Books
A Primer of Playwriting
By Kenneth Macgowan
New York, NY: Random House
1951
Pg. 36:
If it is a comedy, boy meets girl, boy loses girl, and boy gets girl. If it is a tragedy—Romeo and Juliet, for example—boy meets girl, boy gets girl, boy loses girl.
 
Google News Archive
4 August 1952, St. Petersburg (FL) Times,  “The Bess Truman Story” by Inez Robb (INS), pg. 17, col. 2:
The Truman romance meets every requirement of boy meets girl, boy loses girl, boy gets girl.
 
Google Books
Modern Theatre Practice:
A Handbook of Play Production
By Hubert C. Heffner
New York, NY: Appleton-Century-Crofts
1959
Pg. 44:
Boy Meets Girl reiterates its design in the formula: “Boy meets girl, boy loses girl, boy gets girl.”