Camilo is going through a breakup, and he is not handling it gracefully. He admits the split was his fault, "Que se fuera es culpa mía" (that she left is my fault), even though he told her it was "culpa de los dos" (both of our fault). Then come the very modern details: their photo together is still his fondo de pantalla (phone wallpaper), and he keeps going to the places where they used to dance. The saddest little twist is "antes tomaba con ella y ahora tomo es pa' olvidarla" (I used to drink with her, and now I drink to forget her).
The hook, "no se vale", is a phrase worth stealing. It means "that's not fair" or "that's not allowed", the thing you say when someone breaks the rules of a game. And what does he think is unfair? She is posting photos and happy captions, "Te ves más bonita" (you look prettier) without him, while he says "no tengo sonrisa" (I have no smile). He even tells everyone they never broke up, "que es solo un rumor" (that it's only a rumour), then confesses it is a lie. It is petty, honest and very relatable.