Banalisé comes from the verb banaliser, meaning to make something commonplace, ordinary, or trivial. It suggests a loss of specialness or significance.
In "Mal De Nous," Lyna Mahyem sings, "L'amour, on l'a banalisé, ouais" (Love, we've trivialized it, yeah). This word powerfully conveys the idea that the couple has let their love become so ordinary and taken for granted that it has lost its value and intensity, leading to their current struggles.
"Mal De Nous" is Lyna Mahyem and Nassi singing through a breakup that's already happened, not one they're trying to save. The love is still there in a sense, but it's been said too many times, done too much damage, and worn itself out.
The verses walk through the moment two people admit it's over: they've hurt each other, gone numb to it, and there's nothing left to say. The chorus is the ache that lingers after that admission, the void where the relationship used to be, and the realization that thinking about the good times now just hurts.
By the second half, the song makes its case for why leaving is actually the kinder choice: staying would only mean hurting each other more, so walking away, painful as it is, protects what's left of how they feel about one another.