Me arrepiento means "I regret it," from the powerful and emotional verb arrepentirse (to regret). It's a key phrase for expressing a change of heart and is central to the song's story.
In this iconic anthem, Selena sings, "Si una vez dije que te amaba, hoy me arrepiento" (If I once said I loved you, today I regret it). This declaration is the song's emotional core, transforming a memory of love into a powerful statement of empowerment and leaving the past behind.
Ever loved someone so much that when the breakup comes, you feel embarrassed you ever cared? That is the exact punch of Selena's Tejano classic "Si Una Vez". She lays out how she did everything for her partner: "Yo te di todo mi amor y más" ("I gave you all my love and more") and "Yo me puse dispuesta a tus pies" ("I placed myself ready at your feet"). But instead of receiving love in return, all she got was cold rejection ("Y tan solo con desprecio me has pagado" / "And you only paid me back with contempt").
Instead of crying in a corner, she takes all her love back with zero hesitation. The chorus is delightfully blunt: "Si una vez dije que te amaba, no sé lo que pensé, estaba loca" ("If I ever said I loved you, I don't know what I was thinking, I was crazy"). In Spanish, "cosa de ayer" literally means "a thing of yesterday," but idiomatically it means something is completely in the past and dead to you. When Selena sings "Ese error es cosa de ayer" ("That mistake is in the past"), she is drawing a hard line. She warns that he will come crawling back full of regret, but she will never make the mistake of loving him twice.