Años luz literally translates to "light-years". It's a fascinating term because while 'años' means 'years', a light-year is a unit of immense distance, not time.
In this cosmic ballad, Bad Bunny uses the phrase poetically to express the endless nature of his search. When he sings "Yo seguiré buscando mil años luz" (I will keep searching for a thousand light-years), he's saying he would cross the vastness of space to find someone like his lost love, beautifully blending a scientific concept with a feeling of deep longing.
Bad Bunny takes longing into deep space here, and the lyrics get wonderfully ridiculous. He starts out gazing at the night sky and missing an ex with the line "Mirando las estrellas me acordé de ti" ("Looking at the stars, I remembered you"). Wondering if his soulmate is trapped in another galaxy, he decides to tour the solar system to find out. He goes on a date on the moon ("tuvimos un date en la luna"), makes out with an extraterrestrial ("Me besé con un alien"), and even sleeps with female Martians ("tuve sexo con marcianas"). None of it works.
The joke behind all this sci-fi drifting is that his memory of you ruins every single encounter. He admits that he liked his new lunar crush right until he thought of you ("hasta que pensé en usted"). Switching to the formal pronoun usted is a sweet, respectful touch in Puerto Rican Spanish, showing how much reverence he still holds for his past love. By the end, he resolves to keep searching for "mil años luz" ("a thousand light-years"), stuck adrift because no one in the universe beats who he left behind on Earth.