Caballero literally translates to "gentleman" or "knight." It's a classic word that evokes a sense of chivalry and respect, and it's not as common in modern pop lyrics as more casual terms.
In the song, Christian Daniel uses it to express his past behavior in the relationship: "Te extraño, yo contigo fui un caballero" (I miss you, I was a gentleman with you). This highlights his regret and the contrast between his past actions and the current state of the relationship, making it a poignant and interesting choice.
Christian Daniel and Wisin's "Si Pudiera" is a powerful and emotional plea from someone absolutely heartbroken. The singer is writing a letter, feeling like he's "me estoy muriendo en esta soledad" [dying in this loneliness] and can't understand why his former love is attacking him "sin piedad" [without mercy]. He just can't stop missing her, asking, "Dónde está tu sensibilidad?" [Where is your sensitivity?]
He's been left "mal herido, en el suelo destruido" [badly wounded, destroyed on the ground] and desperately wishes he could stop missing her for "un día más" [one more day]. He wants someone to dry his tears so "quizás no doliera tanto" [maybe it wouldn't hurt so much]. The song is full of vivid imagery of his pain, like feeling "demasiada presión, me explota el corazón" [too much pressure, my heart explodes] and how he closes his eyes and still sees her. He's stuck in a loop, trying to forget but fighting with her memory. He asks, "Cómo olvidarme de ti / Si apenas me acostumbra que no estés aquí?" [How can I forget you / If I'm barely getting used to you not being here?]. It's a raw and honest look at the struggle of moving on when you still deeply love someone who's gone.