Lestes translates to "nimble" or "swift". It's a less common adjective in everyday French, making it stand out.
In the song, Julien Doré uses it poetically to describe how friends are "lestes" and "s'envolent avec le vent" (fly away with the wind), suggesting that friendships can be fleeting or change quickly, like something light and agile carried by the breeze. This imagery gives the word a deeper, more melancholic meaning within the context of the lyrics.
"Ami" watches someone change, and reflects on how easily the people we call friends do the same. The singer notices someone close to him shifting with success: chasing status, adopting new values, becoming a stranger to who they used to be ("Tu changes de veste, comme on change de sentiments").
The heart of the song is its chorus: "les amis sont lestes, et s'envolent avec le vent," friends are quick, and they fly away with the wind. It's a plain observation about how loyalty can be fragile, especially once someone succeeds or drifts. What hurts most isn't the leaving itself, it's the absence left behind.
Even with that disappointment, the longing stays ("Tu manques à ma haine, tu manques à mon sang"), even anger can't erase how much you miss someone. It's a bittersweet song about friendship, change, and promises that don't always survive time.