GIGI: A necklace is love/a ring is love/a rock from some obnoxious little king is love./A sapphire with a star is love/an ugly black cigar is love/everything you are is love./You would think it would embarrass all the people here is Paris/To be thinking every minute of love./[…] I don't understand the Parisians/thinking love's so miraculous and grand!
This song establishes Gigi as a child who doesn't know the ways of the world. It's a total mystery to her why people seem to be obsessed with love. Love's been presented to Gigi of a series of ridiculous behaviors and objects that don't seem to make much sense to her. It sets up her character arc and makes her emergence as a young woman in love all that more dramatic. It also lets us see that even as a naïve girl, she has some wisdom about the foolishness of all the pretense in "love."
GIGI: Do you make love all the time?
GASTON: I beg your pardon?
GIGI: Do you make love all the time, Gaston?
GASTON: The only people who make love all the time are liars.
This can totally be read more than one way. On one hand, people aren't making love all the time—they're just pretending they are. On the other hand, they're lying in order to make love all the time, saying anything they need to say in order to "close the deal." Which do you think makes more sense, given the context?
HONORÉ: You're legitimate. He's forbidden fruit.
As Liane canoodles with her skating instructor, Gaston wonders what the instructor's got that he doesn't have. Who knows if Honoré is right; according to him, everyone cheats on everyone and that's just the way it is. Forbidden love is the most exciting of all.
GASTON: Believe or not, Mamita, I have a better time with this outrageous brat of yours than anyone in Paris!
Here's the seed of Gaston's love for Gigi. It's isn't about looks or money or the right cigar. It's about fun and lack of pretense. And no boredom.
AUNT ALICIA: Love, my dear Gigi, is a thing of beauty like a work of art, and like a work of art it is created by artists. The greater the artist, the greater the art.
Aunt Alicia is being practical. This isn't the modern idea of romantic love. Love isn't a feeling—it's a face you create and present to the world.
HONORÉ: I came prepared for battle, and an old wound prevented me from charging.
Comparing love to warfare: oh you old romantic, Monsieur Lachaille!
HONORÉ: I was so much in love with you I wanted to marry you. Yes, it's true. I was beginning to think of marriage. Imagine. Marriage. Me. Ha ha! Oh no, I was really desperate, I had to do something, and there was the soprano!
MADAM ALVAREZ: Thank you Honoré. That is the most charming excuse for infidelity I have ever heard.
Real love was too scary for Honoré and he retreated into a more comfortable life of running around with other women. It's a bit of foreshadowing about what could happen with Gaston and Gigi if he finds himself falling for her.
GASTON (singing): Oh no, overnight there's been a breathless change in you. / […] When did your sparkle turn to fire/And your warmth become desire? / Oh, what miracle has made you the way you are?
Boobs, we're pretty sure. Gigi always had them but they were hidden under her schoolgirl clothes vs. being displayed in her grownup gown. Now Gaston sees her differently. At least Gaston waits for her to look like a young adult before he makes his move. He's the one who's changed, not Gigi. His loving protective feelings for little Gigi have morphed into desire. Notice that he totally projects that onto Gigi.
GIGI: You're a wicked man. You're in love with me and you want to drag me into a life that would make me suffer.
Here's where love really triumphs. Gigi's seen the newspaper headlines and she doesn't want to be an object of scrutiny and criticism like Gaston's other mistresses. She has a more authentic idea about love than anyone in the film. To Alicia and Mamita, love is more a lifestyle than a feeling. Gigi knows that if you love someone, you don't subject her to a life you know she'd hate. You give a darn about what she wants.
AUNT ALICIA: Did you tell her about love, travel, moonlight, Italy, about hummingbirds in the flowers and making love in a gardenia-scented garden?
Does Alicia really believe that love is travel, moonlight, and Italy? Sounds like you don't really even have to like your lover as long as the other conditions are met. In her defense, she's just trying to find a way to convince Gigi to accept Gaston's offer of financial support. Her definition of love worked well for her; she had a cushy life.