Libreto literally translates to 'script', like the written text of a play or movie.
In this heartbreak anthem, Jesse & Joy use it metaphorically to call out a partner's repetitive and predictable excuses. By singing "Tú, libreto de siempre tan predecible" (You, the same old script so predictable), they express that the relationship feels like a tired act they are finally walking away from.
Have you ever been in a relationship that felt like a movie you've already seen? That's the feeling at the heart of "¡Corre!" by Mexican sibling duo Jesse & Joy. The singer has had enough. She describes a partner who looks at her differently and whose hugs have no warmth: "Me abrazas y no siento tu calor" (You hug me and I don't feel your warmth). When she tries to talk, he interrupts, finishes her sentences, and always has to be right. She's completely over his predictable behavior, calling it a "libreto de siempre tan predecible" (an always-predictable script).
So, she tells him to do what he does best: run. The chorus is this powerful command to leave: "Así que corre corre corre corazón / De los dos tú siempre fuiste el más veloz" (So run, run, run, my heart / Of the two of us, you were always the fastest). She's not going to beg him to stay or even cry for him. She tells him to take whatever he wants and just go, declaring, "mis lágrimas jamás te voy a dar" (I'll never give you my tears). It's a final, firm goodbye to someone who has run away so many times before that now, she says, "la verdad me da igual" (honestly, I don't care).