Piedra angular literally translates to "cornerstone", the essential stone that forms the base of a building. It's a beautiful and uncommon metaphor to find in a reggaeton song.
J. Balvin sings "Tu piedra angular" (Your cornerstone) to describe how essential he was to his ex-partner's life and stability. He's reminding her that he was the fundamental piece holding her world together, making his absence all the more impactful.
This song is the ultimate post-breakup anthem for when you're completely over someone. J. Balvin and Bad Bunny team up to tell an ex that it's way too late for a second chance. The main question they keep asking is, "¿Pa' qué me vas a amar?" [Why are you going to love me?]. They've already said their goodbyes and moved on. The title comes from the killer line, "Ahora lo que hagas me vale un peso" [Now whatever you do is worth a peso to me], which is a savage way of saying they could not care less.
They get really specific about why it's over. Balvin says he's heard she's been breaking hearts trying to fill a void, and then drops the incredibly blunt line, "De ti sólo extraño hacerlo sin condones" [The only thing I miss about you is doing it without condoms]. Ouch! Bad Bunny paints a picture of her full of regret, "Pensando en mi mientras el café se te enfría" [Thinking of me while your coffee gets cold]. He reminds her that he adored her and cried for her, but now she needs to find another heart to play with. It's a song about taking your power back and realizing you're better off.