"Mientes" (You Lie) is about the moment you finally see someone clearly. The singer opens by addressing her directly: "Tú supiste encenderme y luego apagarme" (You knew how to switch me on and then switch me off). That on/off image is the whole relationship in one line. She made herself "indispensable", and he followed her "con los ojos cerrados" (with my eyes closed).
Then comes the honest bit: "Si yo busqué dolor, lo conseguí" (If I went looking for pain, I found it). He is not only blaming her; he admits he walked into it. The chorus is about the cycle he wants out of: "Me haces daño y luego te arrepientes" (You hurt me and then you're sorry), and "ya no tiene caso que lo intentes" (there's no point in you trying anymore). A handy phrase to learn here is no tiene caso, a very Mexican way to say "it's pointless". It ends on a clean exit: "hoy estoy mejor sin ti" (today I'm better off without you). Listen for the shout-out in the middle too, "Y es la receta, mija, corridos aesthetic": that is the band name-dropping itself, with mija (short for "mi hija", my girl) as a casual Mexican term of address.