Biromba is a fascinating and somewhat mysterious word in this song. It doesn't have a direct, common translation in Spanish; it's used here as a playful, almost nonsensical sound or piece of gibberish.
In the context of the lyrics, it appears after the line "I was thinking 'bout you, No one else, no one else," suggesting a moment of being lost in thought, perhaps to the point of uttering random sounds or being so consumed by emotion that words lose their conventional meaning. It adds a unique, whimsical, and memorable element to the song, making it stand out.
This is a song about missing one particular person and not being able to think about anyone else. The singer keeps circling back to her, and the question he keeps asking is simply where she is now.
He talks about wanting to hold on to the affection he gave her, and about wounds that still genuinely hurt. Underneath the light, sunny sound there is real loss here. The Malibu of the title is a mood more than a place: an easy, golden style that he tells her suits her perfectly, and that he now associates with her.
In the chorus he runs through the names he has for her and ends up calling her his whole world. When they are together, he says, everything else disappears in a second. He remembers how suddenly it happened, the way she moves, and how he comforted her when she cried. By the end he is still asking the same question, which is what gives the song its ache.