The poem begins with an apostrophe to the speaker's ex, the girl or "Figlia" referred to in the title. It's not immediately clear that she's absent; at first, it seems as though she and the speaker might be in a "garden" together. By the second stanza, however, it's clear that she's long gone, and the speaker is essentially talking to a memory.
It's a strange kind of apostrophe, too: rather than pouring his heart out to the girl, he's giving her instructions. It sounds almost as if he's stage-directing her, or posing her for a picture: "Stand on the highest pavement of the stair," "Lean on a garden urn," etc. He's remembering her, and their breakup, in the way he prefers—making it a prettier scene, or at least one he can live with. The only hint of his underlying passion comes in the repetition of "Weave, weave the sunlight in your hair."
Finally, "Weave, weave the sunlight in your hair" (repeated twice in the first stanza) is a visual metaphor. It describes a delicate play of light and shadow in the girl's hair, such that the two seem woven together. It's a lovely, subtle image that conveys how the speaker wants to remember her: beautiful and perfectly posed.
Even more unusual is the way the apostrophe ends after the first stanza. The speaker shifts to critiquing his breakup, alternately referring to himself in the third and first person as he does so. It's as if he's switching psychological tactics while coming to grips with a painful event. Meanwhile, he shifts from addressing his ex in the second person to recalling her in the third. This change makes her seem all the more distant, underscoring the fact that their romance is truly over.