The speaker wants to live in light but can't seem to get there. They can see it clearly, "sure as hell," yet only a thin sliver ever reaches them, wrapping around their waist like tiny fingers. That image is gentle but frustrating: the light is close enough to touch and never close enough to fill them up.
Darkness, meanwhile, keeps interrupting. Each time the speaker reaches for light, darkness grabs and kisses them, which is where the title "french kisser" comes in. The kiss is intimate rather than violent, and that makes it more unsettling, since it suggests darkness is a familiar pull the speaker can't easily resist. Light is left "heartbroken and gone," as if the speaker has hurt it too.
The mood is wistful and quietly pleading. The final lines speak to light directly, hoping it returns so darkness shrinks to a sliver. The speaker wants the proportions reversed.