Rehacer literally means "to remake" or "to redo." It combines the prefix re- (again) with the verb hacer (to make/do).
In this song, Camilo uses it in the powerful phrase "rehacer tu vida" (to rebuild your life), which means to start over after a significant setback. The emotional core of the song is revealed when he accepts his ex will move on, but then heartbreakingly confesses "yo no puedo rehacer la mía" (I can't remake mine), expressing that he's completely stuck in the past.
This song from Colombian artist Camilo is one of the most dramatic breakup songs you'll ever hear. He's so heartbroken that when he tells the sky his partner left, the sky literally starts to cry: "Le dije al cielo que te fuiste y empezó a llorar" (I told the sky you left and it started to cry). He's full of regret, wishing he could have done everything differently and admitting he hid his flaws, begging for forgiveness: "Perdóname por no mostrarte todos mis defectos" (Forgive me for not showing you all my defects).
He mixes these huge, poetic feelings with really specific, modern details of a breakup. He pinpoints the exact moment his heart was broken as "El día que le borraste a mi contacto el corazón" (The day you deleted the heart from my contact). He's also terrified of the future, imagining the pain of seeing her post a photo "en los brazos de un extraño" (in the arms of a stranger). It's a song about someone who feels like he can't move on and is desperately hoping his ex feels even a little bit of the same pain.