Rain falls on the speaker's face, and as it runs down it seems to turn red. From the start, beauty and pain are mixed together. Flowers remind the speaker of thorns, and holding on tightly means bleeding. The "glass flower" is the center of it all: a woman, it seems, who is lovely and fragile but cannot be touched without causing a wound. The speaker calls her "my sweet poison," and the phrase sums up the whole feeling of wanting something that hurts.
What the speaker feels is stubborn devotion. They stand in the storm, ready to be consumed by their own river of pain, and promise not to flinch in order to protect her. Yet there is heartbreak too: she may see them only as an illusion, and what they catch are reflections, not the real person. Even so, the speaker longs for the next bloom and another taste of that poison. The mood is dark, romantic, and a little reckless, a mix of tenderness and self-destruction.