Balero is a traditional Mexican toy, similar to a cup-and-ball. It consists of a wooden cup and a ball connected by a string, with the goal of skillfully catching the ball in the cup.
In the song, the artist uses it as part of the classic, playful taunt, "Lero, lero... como balero". This phrase is like the English "na-na na-na boo-boo", adding a uniquely Mexican and dismissive tone to his message for his ex, making it a very memorable and culturally specific insult.
This song is a whole rollercoaster of post-breakup feelings. Tito Double P starts off trying to sound tough, telling his ex, "Ya no llames, bebé" (Don't call anymore, baby). He's bragging about finding new, better lovers and warns her to stay away so he doesn't have to treat her "como si fueras nadie" (as if you were nobody). He's all about partying and drinking to forget her, with Dom Pérignon champagne and cherry weed everywhere.
But then, the tough guy act starts to crack. He admits that being with someone else just makes him think of her, remembering intimate moments under the full moon. The most revealing part is when he says, "Por ti el polvo iba a dejar" (For you, I was going to quit the powder), but she left for someone else who she thought would value her more. He's hurt that she didn't see "Todo el amor que yo te daba" (All the love that I gave you), and the song ends on a sad, final note: "Todo lo que empieza también algún día se acaba" (Everything that starts also ends one day).