Poner el cuerno literally translates to "to put the horn on". It's a colorful and common Spanish idiom used to say that someone is being unfaithful in a relationship.
In the song, the singer warns his ex, "Te pone el cuerno y no te enteras" (He cheats on you and you don't even find out). This dramatic accusation is his way of proving that she made a mistake by leaving him for her new partner.
If you have ever watched an ex downgrade to someone who treats them horribly, this track by Mexican stars Carin León and Gabito Ballesteros is your new anthem. The entire song is a blunt, petty, and brutally honest reality check aimed at an ex-lover. León watches her rush into a rebound, begging her to slow down with "Bájale, porfa" (Slow it down, please) because she is moving "a mil por hora" (at a thousand miles an hour) only to end up "de mal en peor" (from bad to worse). The title and main hook say it all: "A ti ese vato no te queda" (That guy doesn't suit you / That dude is not on your level).
The lyrics are packed with punchy Mexican slang that makes the jealousy feel hilariously unfiltered. He swears he is speaking "al chile" (honestly / strictly the truth) and insists his rant is "no es por ardido" (not because I'm bitter or salty), even though he clearly is. He roasts the new partner as a nobody who "no me llega ni a los zapatos" (can't even reach my shoes / isn't on my level) and laughs at how the guy "te pone el cuerno y no te enteras" (cheats on you and you don't even notice). It is a proud, funny, and direct track celebrating bruised egos and total refusal to admit your ex upgraded.