Tropiezo literally means "stumble" or "trip." It's a vivid word that can also be used metaphorically to mean a "setback" or a "mistake."
In the context of the song, the singer uses it to refer to his ex-partner's mistake or misstep in their relationship, saying, "Diste un tropiezo y trataré de ser el fuerte" (You made a mistake/stumbled, and I will try to be the strong one). This word captures the emotional weight of a relationship gone wrong and the effort to move past it.
This song is all about that terrible moment after a breakup when you don't know what to do next. The singer asks the big question right in the title: "Llamarte o bloquearte, ¿será bueno?" (Call you or block you, would it be good?). He can't get her out of his head, and it's made worse because he sees her on social media, smiling with a new guy: "Veo tu historia y miro lo peor de lo peor / Tu sonrisa con otro" (I see your story and I see the worst of the worst / Your smile with another). He thought she was the woman of his dreams, but now he feels like "Todo fue un juego" (It was all a game).
It gets even more personal when he mentions his mom asking if she's coming over, showing how much a part of his life she was. He's angry at her new choice, calling the other guy a "cobarde" (coward) who will treat her badly. He feels he was the loyal and honest one, but she chose someone else. In the end, he decides he has to face being alone, saying, "Yo probaré la soledad por un buen tiempo" (I will try out loneliness for a good while).