Just got done with this musical (I played Ruth), and I can help you out here.
Lenoard Bernstein wrote the score in 4 weeks AFTER Comden and Green had written the lyrics. I am not sure what the whole inspiration was for the song (lyrics anyway), but in the context of the show, Eileen sings the song, the WHOLE SONG first after Frank Lippencot shows up with some chocolates for her. Then, after she sings, Bob Baker comes in looking for Ruth after reading her stories, and she sort of confuses the audience into singing a reprise of the song. Essentially, she likes both guys, but in the end of the show, ends up with niether (our director interpreted it that way, while other directors may have her end up with Frank, sort of like in the movie verion, MY SISTER EILEEN).
There you go!!!
Hope that helped!
"What do you think of our double malts, family vaults, Epsom salts? Wouldn't you guys like to learn the waltz? Nah, you just want to CONGA!"
-Ruth Sherwood ~ Wonderful Town