Fidel Rueda sings a thank-you note to the person who turned his luck around. It opens with "Acabaste con mi mala suerte" (You put an end to my bad luck) and "Cambiaste todo mi destino" (You changed my whole destiny), so from the first line this is a man who feels rescued.
My favourite image is "Y le pusiste sal y pimienta a cada día que vivimos" (And you put salt and pepper on every day we live). It is a kitchen phrase: "ponerle sal y pimienta" to something means adding flavour and spark, so his days used to be bland and now they taste of something. He is so happy he admits "ahora me ando riendo solo" (now I go around laughing to myself), which is a lovely, slightly goofy detail.
The chorus gets bigger: "A diario me llevas al paraíso" (Every day you take me to paradise), the regrets are gone, and when he kisses her "el tiempo se detiene" (time stops). The title line lands at the end: "Que no sé cómo pagarte" (That I don't know how to repay you). Listen for "pagarte", which literally means "to pay you"; here it is about a debt of gratitude, not money.