Armamento translates to "armament" or "weaponry". It's an intriguing word choice in a song about a relationship, as it immediately sets a dramatic and combative tone.
In the lyrics, Paula Arenas sings, "Ahora que no tengo el armamento ¿cómo gano esta batalla?" (Now that I don't have the armament, how do I win this battle?). She uses this word metaphorically to describe the emotional tools or defenses she once had in the relationship, now lost, leaving her vulnerable in the "battle" of her memories and regrets.
Paula Arenas opens this one already mid-argument with herself: "Ahora que no tengo el armamento ¿cómo gano esta batalla?" (Now that I don't have the weapons, how do I win this battle?). She keeps score just as bluntly a few lines later: "Tú sumabas todo" (You added everything). "Y yo siempre restaba" (And I always subtracted). By the second verse she's stopped fighting it and just admits "ya de lo que fue no queda nada" (nothing remains of what was).
The chorus doubles as the title and the whole thesis: "Puedo ser muy buena" (I can be very good). "O buena para nada" (Or good for nothing). It's a shrug, not an apology. She owns the lie outright, no excuses: "Si te mentí, te lo advertí, ¿qué esperabas?" (If I lied to you, I warned you, what did you expect?). There's no villain in this one, just someone who knows exactly which parts were on her and isn't asking to be let off the hook for them.