Malgastaba comes from the verb malgastar, a powerful combination of mal (bad) and gastar (to spend). It means "to waste" or "to squander," implying spending something precious carelessly.
In the song, the singer describes his state after the breakup: "Yo malgastaba los segundos" (I was wasting the seconds) while his ex was traveling the world. This single, evocative word paints a vivid picture of being stuck in heartbreak, watching time slip away uselessly.
This song is the ultimate anthem for when an ex suddenly reappears after they were the one who left. Morat lays it all out on the table from the very first line: "No hay más que hablar" (There's nothing more to talk about). The singer is completely baffled that this person has shown up at their door, "Con la certeza de que sigue abierta" (With the certainty that it's still open), as if nothing happened. He reminds them that it was their choice to leave, asking, "Si hay tantos peces en el mar / ¿Hoy por qué vuelves a buscar / Algo conmigo?" (If there are so many fish in the sea / Why are you coming back to look for / Something with me today?).
What really makes this song hit is the contrast between what they were both doing during the breakup. While the ex was off living their best life, "de fiesta en Barcelona / Jugando a ser otra persona" (partying in Barcelona / Pretending to be someone else), the singer was stuck at home, "Dando mil vueltas en la cama sin dormir" (Tossing and turning a thousand times in bed, sleepless). But the pain is in the past. He's not the same heartbroken person they left behind. He makes it clear he's moved on with the powerful line, "Yo no cambié / Sólo aprendí a vivir sin ti" (I didn't change / I just learned to live without you).