Olvidarte (Forgetting you) is a love song built on one long, bitter joke. Every verse opens with "Olvidarte será fácil, ya lo sé" (forgetting you will be easy, I know), and then lists what it would take: "dejar de ver el mar" (stop seeing the sea), go blind to the starlight, never watch the moon rise behind a window again. By the second verse he would have to tear you "de mi piel" (from my skin) and shut every door and window so neither night nor dawn gets in. Easy, sure.
The lines get more impossible as they go. "Tapar el sol entero con un dedo" (cover the whole sun with one finger) is a real Spanish saying for trying to hide something obvious, and here it is one more thing he would have to pull off. He would also need to "cambiar mi corazón por uno de papel" (swap my heart for a paper one). The last line lands hardest: forgetting you is just a matter of "olvidar que he nacido" (forgetting I was ever born). Watch for tengo apenas que (I only have to), which repeats all song long and is a useful way to say "all I have to do is".