Two short lines carry a lot of hurt. The speaker is talking directly to "you," someone they love deeply, and says that person is everything they could ever want. But the second line turns it around: "you" only wants "her." The speaker is left on the outside, caring for someone whose attention is already taken.
The poem works because of one small repetition. "Ask" appears in both lines, first as what the speaker could want, then as what the other person actually wants. The speaker's feelings and the other person's are lined up like a mirror, and neither one meets the other. There is no anger here, and no begging. The tone is quiet and resigned, almost matter-of-fact, which makes the pain feel more real.
The mood is wistful and a little bitter. The title, in lowercase and quotation marks, makes the poem feel like a private message that might never be sent. It captures the helplessness of unrequited love: the speaker has already said everything they have to say.