Valser literally means "to waltz", the elegant ballroom dance. It's a word that evokes images of grace, romance, and spinning motion.
In the song, M. Pokora sings, "À toi, qui fait valser mon coeur" (To you, who makes my heart waltz). He uses this beautiful verb metaphorically to describe the powerful, dizzying effect someone has on him, as if his heart is being swept away in a dance. It’s a much more poetic and memorable image than just saying his heart is beating fast.
M. Pokora's "Si T'es Pas Là" starts like a classic love song, with him spending nights dreaming and feeling like his past songs were meaningless because they weren't for this special person. He uses some big comparisons to describe a life without them: it's like "un monde sans ciel" (a world without a sky) or "l'amour sans ailes" (love without wings). Everything feels empty and pointless if this person isn't there.
But then the lyrics give us a huge clue about who he's singing to. He sings about waking up and seeing "que tout a changé / Petit dans mes bras" (that everything has changed / Little one in my arms). This isn't about a romantic partner, it's a powerful song from a father to his child! He talks about becoming fragile and "trembler comme une feuille" (trembling like a leaf), which perfectly describes the overwhelming and vulnerable feeling of holding your own kid for the first time. It's a sweet twist that turns the song into a beautiful declaration of fatherly love.