Círculo vicioso translates to "vicious circle." It's an idiomatic phrase that describes a situation in which one problem leads to another, which then aggravates the first problem, creating a continuous loop.
In the song, Raymix uses this phrase to describe the frustrating and repetitive pattern of unrequited love and emotional complications. He sings about breaking this "tonto círculo vicioso de amor" (silly vicious circle of love), making it a central and memorable theme of the song.
Have you ever felt stuck in a ridiculous love triangle? Raymix's "El Círculo" [The Circle] totally gets it! He kicks off by wondering why we love to suffer and cry, making things super complicated. He's like, "Yo me pregunto porque será / Nos gusta sufrir nos gusta llorar / Complicamos las cosas hasta el más allá" [I wonder why it is / We like to suffer, we like to cry / We complicate things to the extreme]. He just doesn't understand why we're not happy and why we always love someone who doesn't love us back, ignoring the person who does care.
He describes this frustrating cycle perfectly: he wants to be with a girl, but she likes some other guy. And that guy is into a different girl who, ironically, is totally into Raymix! He sings, "Me busca a mí / Me quiere a mí / Muere por mí / No me interesa su amor" [She looks for me / She loves me / She dies for me / I'm not interested in her love]. It's a never-ending loop! He just wants to make things easy: "Te amo, me amas / Tan simple como eso" [I love you, you love me / As simple as that]. He's ready to break this "tonto Círculo vicioso de amor" [silly vicious circle of love]. Can you relate?