Desahuciado is a powerful word with a double meaning. It literally translates to "evicted", as in being kicked out of a home, but it's also used to describe a medical patient who is "given up for lost" or is considered terminal.
In the song, the singer uses this word metaphorically to describe how he felt in the relationship: completely hopeless and cast aside. It's a dramatic and uncommon word that perfectly captures the feeling of utter devastation before he found the strength to move on.
This is the ultimate getting-over-you anthem from Mexican rock legends Maná. The singer starts by describing a relationship that was completely one-sided. His ex was destructive, "matando mis pasiones" (killing my passions) and had him "pisoteado" (stepped on). He was a total mess, crying so much he says, "te lloré todo un río" (I cried you a whole river).
But then comes the big shift! The world has turned, and he's not sad anymore. He's moved on and found someone new, who he calls "una chula sirena" (a beautiful mermaid). The best part is the final message to his ex. Now that she wants him back, he tells her, "Te lloré todo un río / Ahora llórame un mar" (I cried you a whole river / Now you cry me an ocean). It's a powerful and satisfying comeback, telling her that it's her turn to feel the pain, but even more.