Pacto translates to "pact" or "agreement." It's a word that carries significant weight, implying a serious, often solemn, understanding or promise between individuals.
In the context of "MORIR TRES VECES," the singer desperately hopes their love will return to fulfill "nuestro pacto" (our pact). This suggests a deep, shared commitment or promise that was made between them, making the word intriguing and hinting at a dramatic backstory to their relationship.
The song runs on bad timing. She has already closed the book — Que esta novela ya llegó al final ("That this drama has already come to an end") — while he is only now admitting how far in he is: Ahora que te has clavado bien en mí ("Now that you've gotten so deep under my skin"). Every verse sets her leaving against his arriving, and he asks for another chance while answering himself before she can: Que a ti volver eso no se te da ("That coming back isn't your thing").
What she offers instead is comfort, and he will not take it. Me dices que ya no / Que se me pasará ("You tell me not anymore / That I'll get over it") is the gentlest exit line there is, and the title is his refusal of it: Moriré tres veces y, tal vez / Regreses a mis brazos y cumplir nuestro pacto ("I will die three times and, perhaps / you'll return to my arms to fulfill our pact"). Three deaths set against a perhaps — he is not negotiating the price, he is naming it. Then he hands her the good part on the way out: Y te dejo con las tardes que yo te robé ("And I leave you with the afternoons that I stole from you").