The speaker is worn out by hiding their pain. On the surface, everything looks fine: they seem happy and life seems in order. Inside, they say they are "dying" and craving something else to fill the emptiness. The poem even touches on the thought of ending it all, then circles back to the refrain "Not any more," as if the speaker keeps trying to draw a line and say enough.
The refrain does odd work, though. Each time it promises change, the next lines show the pain returning. The central image is the bottle sent to sea: the speaker tries to get rid of their feelings, but the bottle drifts back to their "leaking boat." The ending is bleak. The speaker lets the ship sink, admitting things are getting worse, not easier. The mood is raw, tired, and desperate, and the closing "Not anymore...." trails off in a way that feels unresolved rather than hopeful.