Fol is an archaic or poetic form of fou, meaning "mad" or "crazy." It's a captivating word that immediately draws attention due to its slightly unusual spelling and strong emotional connotation.
In "Mon Fol Amour," Indila repeatedly uses "mon fol amour" to describe a love that is passionate, intense, and perhaps a little irrational or overwhelming. It evokes a sense of a love that defies logic and leaves a lasting, almost haunting, impression, making it a very memorable and enticing word from the lyrics.
This song is a beautiful, bittersweet farewell to a powerful love. Indila isn't crying or angry; she's looking back on a relationship that has ended with a lot of maturity. She describes it as her "fol amour" [crazy love], a love that was intense and life-changing, but now it's time to say "un dernier adieu" [a final goodbye]. They are facing the end directly, "Sans une larme qui coule / Sans détourner les yeux" [Without a tear falling / Without looking away].
Even though they are parting ways and will likely find new partners—"Ayant refait nos vies dans d'autres bras" [Having remade our lives in other arms]—the memory of this love is permanent. She says it's impossible to simply erase the past. Instead, this love has dug "un sillon profond" [a deep furrow] in her heart. She promises to carry the memory of her "merveilleux et délirant compagnon de parcours" [wonderful and delirious companion on the journey] forever, like a secret garden she can always return to.