The speaker has already let go of love and friendship—she calls them things relinquished long ago. What she wants now is smaller and stranger: a little boat, a calm drift, and then a silent sinking into quiet seas. It is a wish for peace, but also for disappearance, a slow fading rather than a dramatic end. There is no bitterness in her voice, only exhaustion and a kind of relief that she no longer expects much from life.
The title, Lethe, is the river of forgetfulness in Greek myth, and that fits the mood perfectly. The speaker seems to crave forgetfulness or release from memory, emotion, and connection. The poem feels hushed and resigned, like someone speaking from the far side of disappointment, not asking to be saved, only to be allowed to rest and slip away.