Me arrepiento comes from the reflexive verb arrepentirse, which means "to regret" or "to be sorry for". It's a powerful, emotional word that expresses deep remorse over a past action.
In the song, Aitana sings, "Dile que en la noche a veces me arrepiento" (Tell him that at night, I sometimes regret it). She uses this phrase to confess her lingering feelings and reveal the profound regret she feels about ending their relationship, making it the heart of the song's message.
“Cuando hables con él” is Aitana’s heartfelt voice note to a mutual friend, mixing nostalgia, regret, and tenderness in one breath; she asks that friend to pass along a simple hola while secretly unloading a suitcase of emotions: she hopes her first love is happy, admits she dated someone else (but no, she is not lonely), confesses she still thinks of his blue eyes at night, and owns up to the “stupidity” of letting him go; yet, even in this rain of feelings, she insists on protecting him from more pain, proving that first loves leave marks that even catchy pop hooks cannot erase.