Bobo da corte literally translates to "court jester". It's a colorful and somewhat archaic phrase that evokes images of medieval royalty and entertainment.
In the song, the singer uses this phrase to describe his transformation from a
Melim opens by admitting the plan fell apart: "Era pra ser outra canção feliz" (It was supposed to be another happy song). He meant to write something upbeat this time, and the breakup took over instead.
He leans on a chess metaphor to explain what happened: "Paguei pra ver, joguei xadrez / Perdi minha rainha achando que eu era rei" (I took a chance, I played chess / I lost my queen thinking I was king). He got too comfortable acting like the king of the relationship, and lost the queen because of it. She "foi-se embora como se não fosse voltar" (went away as if she wouldn't return), and he saw none of it coming: "Nem dei ideia" (I didn't even care).
By the end he's paying for it. "Sem conseguir dormir à noite" (Without being able to sleep at night), the king has turned into the fool instead: "O rei virou bobo da corte" (The king turned into a court jester). The closing image is simple and a little theatrical, "Minha guitarra chora" (My guitar cries), right before the song loops back to that opening line, still not the happy one he wanted to write.