Arrepientes means "you regret" and comes from the reflexive verb arrepentirse. Reflexive verbs are a key concept in Spanish where the action reflects back on the subject, making this a great word to learn.
In this classic song, Selena confronts her ex-lover, singing, "Ahora te arrepientes, ya ves" (Now you regret it, you see). This is the powerful turning point where she points out that he's the one left with regret, perfectly capturing the song's defiant and heartbroken tone.
This is the ultimate song for when an ex comes crawling back after they're the one who messed things up. Selena is completely over a guy who left her "Sin motivo y sin razón" [Without motive and without reason]. She says she was wrong to ever believe in him, because all he ever gave her was betrayal, singing "Tú heriste mi corazón" [You hurt my heart].
But now the tables have turned. He's full of regret, and she's not having any of it. The whole chorus is a fantastic taunt, repeating "Ya ves" [You see] to rub it in his face. She asks him directly, "Dime, ¿cómo se siente / Que ya no te quiero?" [Tell me, how does it feel / That I don't love you anymore?]. The final burn is perfect: she tells him that now, all he has left is himself and his pride: "Nomás se quedaron solo tú y tu orgullo" [Only you and your pride are left].