Atorrante is a fantastic piece of slang, primarily from Argentina, that means "scoundrel," "rogue," or "good-for-nothing." It describes someone who is lazy, shameless, and lives a carefree, often irresponsible life.
In the song, the singer uses this word to confess his past mistakes. He calls himself an atorrante to admit he was a foolish and arrogant person who took his partner's love for granted, making it the central theme of his apology.
This song is a massive apology from a guy who knows he messed up badly. He calls himself an "atorrante" (a scoundrel), an "ladrón elegante, tonto y arrogante" (an elegant thief, foolish and arrogant) who completely blew a good relationship because he was too busy partying and was afraid of love. He's brutally honest about his faults, admitting he was "perdido y de fiesta / Viviendo de noche y pasado de alcohol" (lost and partying / living by night and drunk). Now that she's gone, he's begging for forgiveness and insisting he's not that same fool anymore.
His regret is pretty intense. He feels "solo y arrepentido como un perro" (lonely and repentant like a dog) and is crushed to see on social media that she has a new boyfriend who is "más lindo que yo" (better-looking than me). He's tried everything to get her attention, from dedicating love songs to her for months to drunk-texting her from a bar. He knows her friends hate him, but he swears he's changed. Still, he's stuck in a loop, kissing strangers just to try and forget her, but admitting "y no será" (it won't happen).