Cegó comes from the verb cegar, meaning "to blind." It's a strong verb that you don't encounter in every song, making it quite impactful.
In the song, the singer admits, "Mentí, mentí, mentí porque el orgullo me cegó" (I lied, I lied, I lied because pride blinded me). Here, cegó is used metaphorically to express how his pride prevented him from seeing clearly and acting truthfully, leading him to lie to the person he loves.
Have you ever said something you didn't mean, all because your pride got in the way? That's exactly what Remmy Valenzuela is singing about in "Mentí" [I Lied]. He tells his love to leave him alone, saying he doesn't feel anything anymore and that he could never forgive her. He even says, "Le pedí que se olvidará de que existo" [I asked her to forget that I exist] and to never call him because he's her ex, not her friend.
But then comes the big reveal: "Mentí, mentí, mentí porque el orgullo me cegó" [I lied, I lied, I lied because pride blinded me]. He admits he lied because she didn't value his love, and even though she failed him, he still loves her. He's dying to see her again, even after telling her he never wants to hear from her. It's a really relatable song about how our pride can make us say and do things we immediately regret, especially when we're heartbroken.