No Eras para Mí is a calm, grown-up breakup. Carlos Rivera is not shouting at anyone here. He looks back at a couple who kept asking "cuántas veces" (how many times) they tried to find a reason not to walk away, and how often they "disfrazamos la rutina del amor" (we disguised the routine of love) while it was killing the heart "poco a poco" (little by little).
The chorus asks a sharp question: "¿para qué seguir pintando de color un cielo gris?" (why keep painting a grey sky in colour?). That is the whole song in one image, and it works. So he says "mejor suelta ya mi mano" (better let go of my hand now) and lands on the line that gives the song its name: "tú no eras para mí, yo no era para ti" (you weren't meant for me, I wasn't meant for you). For a learner, notice eras and era: the imperfect tense, used for how things were all along, not one moment.