Desenamoré is the past tense of the verb desenamorarse, which means 'to fall out of love'. It's a powerful and specific verb that captures the painful process of losing feelings for someone.
In this song, the artist uses it to express a definitive end to a toxic relationship: "Fueron tantas mentiras tontas que me desenamoré" (There were so many silly lies that I fell out of love). It's a less common and more impactful way to say 'I stopped loving you', making it particularly memorable and relevant to the song's theme of moving on from a hurtful past.
This song is a powerful anthem for anyone who has finally gotten over a bad breakup. Emanero and Angela Leiva trade verses about a relationship that caused nothing but pain. The singer says they suffered what "nadie merece sufrir" (no one deserves to suffer) and even cried "más que un río" (more than a river). They felt like they lost themselves trying to change their partner, and realized it was impossible to live like that.
But now, everything has changed. The ex is in the past, and the singer declares, "Yo no siento más dolor" (I don't feel any more pain). The best part is the total shift in power. The ex can call and beg, but as the chorus states, "eso no va a arreglarme el corazón" (that's not going to fix my heart). The singer has realized their ex wasn't so great after all and has finally moved on. Now, it's their turn to watch the ex cry, "queriendo volver" (wanting to come back).