Queixo-me comes from the verb queixar-se, meaning 'to complain' or 'to lament'. It's a reflexive verb, which adds a layer of introspection to the act of complaining.
In the song, the singer says, "Queixo-me às rosas" (I complain to the roses). This personification of the roses, treating them as confidantes for his sorrow, makes the word particularly evocative and sets a melancholic yet poetic tone for the lyrics.
"As Rosas Não Falam" is a tender, wistful love song about heartbreak that never turns to anger. The singer keeps returning to the garden he shared with someone who no longer wants him back, and each time the roses knock at his heart again, reopening the wound.
He confides his sadness to the roses, half-embarrassed at himself for it ("mas que bobagem", "but how silly"), because the roses can't answer him. They can only exhale their perfume, the same perfume he imagines was stolen from the one he loved. He wishes she could see how sad his eyes have become, and wonders if she still dreams the same dreams he does.
It is a simple, delicate metaphor for lingering love: the garden keeps blooming and the memory keeps knocking, even when the person is gone.