Me arrepiento means 'I regret it'. It comes from the reflexive verb arrepentirse, a powerful word used to express deep remorse or regret for something you have done.
This phrase is the emotional core of the song. The singer declares that if he once said he loved someone, 'hoy me arrepiento' (today I regret it), marking a dramatic turning point from past love to present-day regret.
Have you ever looked back on a relationship and just thought, what was I thinking? That's exactly what this song is about. Carin Leon sings about a love where he gave everything, saying, "Yo te di todo mi amor y más" (I gave you all my love and more). He put himself at his lover's feet, but all he got in return was disrespect. It's a powerful song about realizing you deserved better.
The best part is the total change of heart. The chorus is a blunt rejection of his past feelings: "Si una vez dije que te amaba, hoy me arrepiento" (If I once said I loved you, today I regret it). He even calls himself crazy for ever feeling that way! He's completely done with it, declaring that mistake is a "cosa de ayer" (thing of the past). The song ends with a confident prediction: he knows his ex will come back one day, full of regret, but it will be too late.