Aferres comes from the verb aferrarse, which means "to cling to" or "to hold on to something tightly". It's a powerful reflexive verb that implies a desperate, emotional attachment.
In the song, the singer pleads, "No te aferres, ya no te aferres a un imposible" (Don't cling, don't cling to an impossibility anymore). He uses this word to ask his former lover to stop holding on to a past that can't be revived, perfectly capturing the pain and struggle of letting go.
Ever had an ex show up out of nowhere, expecting to pick things up right where you left off? That's the messy situation at the heart of this song by Argentine reggae artist Dread Mar I. He's talking to a former lover who has returned, but it's too late. He's trying to apologize for the pain this will cause, saying "Perdona si te hago llorar" (Sorry if I make you cry), but he's not taking them back.
The reason is simple and direct: "Me he enamorado" (I have fallen in love) with someone new. He's brutally honest about it, telling his ex, "A ella la quiero, a ti te he olvidado" (I love her, I have forgotten you). He reminds them that they were the one who left without a word, and now he's found a "buen amor" (a good love) who taught him how to move on. He tells them not to cling to an impossible dream—"No te aferres... a un imposible"—because for him, that chapter is completely closed.