Rompecabezas literally translates to "head-breaker", but it's the common Spanish word for "jigsaw puzzle". It's a fun and evocative word that paints a clear picture.
In the song, the lyrics "Junta pedazos de un amor como un rompecabezas que me dejaste" (Put together pieces of a love like a jigsaw puzzle you left me) use this word to beautifully describe the fragmented nature of a broken relationship, where the singer is trying to piece together what's left.
Kalimba wakes up with his heart doing all the talking here. It won't let him pretend he's fine, so the song opens mid-argument with himself: "Grita que no estoy yendo a ninguna parte" (it screams that I'm not going anywhere). He'd been asking time to just let him move on, and it isn't working; something keeps pulling him back to look for her, wherever she went.
The title comes from the hook he repeats after every chorus, "Estrellas rotas solo espérame" (broken stars, just wait for me), and it reads like a promise he's making to himself as much as to her. He isn't asking her to fix anything alone. He says he'll run to catch up to wherever she is and "yo voy a reparar" (I'm going to repair it), putting the work on himself. By the bridge, when hope has run out of wings and air to breathe ("sin alas y sin fuerza para respirar"), he still calls her the light in the storm. It's a song about refusing to let go, less because he's sure it'll work than because giving up feels worse.