Comerá is the future tense of the verb comer, which literally means "to eat". So, comerá translates to "it will eat".
In this classic ballad, Enrique Iglesias uses this word in a powerful and dramatic metaphor: "El dolor me comerá" (The pain will eat me). He's not talking about literal hunger, but about being completely consumed and overwhelmed by the emotional pain of his lover leaving. This striking imagery makes it a very memorable line.
This is a classic '90s pop ballad from Spanish superstar Enrique Iglesias, and it's all about the absolute terror of being left by someone you love. He's not describing a breakup that has already happened; he's imagining it. The whole song is built on his fear that "algún día llegará" [the day will arrive]. He feels that if his partner leaves, his life will completely fall apart. He says he won't know where to go and that "el dolor me comerá" [the pain will eat me].
He really goes for it with the dramatic imagery. The most memorable part is when he declares, "Mis lágrimas hacen un mar / Nadaré sin descansar / Esperando tu llegar" [My tears make an ocean / I'll swim without resting / Waiting for you to arrive]. It's such an over-the-top and desperate picture of him literally swimming in an ocean of his own tears, hoping she'll come back. It's the kind of huge, emotional declaration that made him a global star.