Tropezón literally translates to "stumble" or "trip." It's an interesting word because it implies a mistake or error, but often one that is accidental or not entirely intentional.
In this song, the singer uses "un tropezón" to describe his infidelity, downplaying it as a mere misstep rather than a deliberate act of betrayal. He's trying to convince his partner that it was just a momentary lapse, not a true change of heart, making it a key word for understanding his plea for forgiveness.
Have you ever messed up so badly that you just can't stop thinking about it? That's exactly where the singer of Los Alameños De La Sierra's "El Tropezón" is. He's spending all day and night "maldiciendo" [cursing] because he doesn't have his love anymore. He misses her so much, calling her "mi vida" [my life] and "mi mujer" [my woman].
He totally owns up to his mistakes, saying "reconozco que yo te he fallado" [I recognize that I have failed you] and he's really sorry if he hurt her. He feels like he's paying a high price for comparing "la sal con la miel" [salt with honey]. He desperately wants her to know that what happened was just "un tropezón" [a stumble] and not that he actually changed her for someone else. He's begging for another chance, promising "nunca más te fallaré" [I will never fail you again] and that he'll "portar bien" [behave well]. He even fondly remembers their first time together "allá en el arroyo" [there by the stream], when she told him he was everything and she'd never lose him. It's a really heartfelt plea for forgiveness and a second chance!