Arrepentida means 'regretful' or 'sorry', but it conveys a much deeper sense of remorse than a simple apology. It's the feminine form of the adjective derived from the verb arrepentirse, which means 'to repent' or 'to regret'.
In the song, Aitana sings, "Yo que me acostumbré a estar arrepentida" (I, who got used to being regretful). This powerful line reveals she has lived with this heavy feeling for a long time, making her plea for a second chance incredibly sincere and heartfelt.
Have you ever been so scared to admit you're in love that you end up pushing the person away? That's exactly what Aitana is singing about in this powerful pop ballad. She starts by taking all the blame, admitting, "Yo sé que fue por mi que acabó esta historia" (I know it was because of me that this story ended). She knew she was in love but kept it a secret, and now she's full of regret and can't stop thinking about him.
This whole song is basically her big, dramatic plea for a second chance. She's done hiding her feelings and is ready to fight for him. The chorus is so determined, repeating "Vas a quedarte" (You're going to stay) like she's trying to will it into existence. She promises, "te juro que esta vez voy a cuidarte" (I swear that this time I'll take care of you), and insists their love story needs a sequel, even if everyone says second chances are a bad idea. It's a song about realizing you made a huge mistake and being willing to do absolutely anything to fix it.