The speaker describes a kind of restless desperation: the urge to keep moving, to cover thousands of miles, in the hope that distance might loosen the grip of an inner hurt. The image of walking is simple, but the number says a lot. Thousands of miles is far more than anyone could really manage, so the exaggeration shows how badly the speaker wants relief.
What follows is the heart of it. "It never works, it stays..." The pain is described as "overflowing deep inside," which suggests something too big to contain, yet also something buried where no journey can reach. Walking can change where you are, but not what you carry.
The mood is weary and quietly hopeless. The trailing dots at the end leave the thought unfinished, as if the speaker is too tired to say more, or as if the pain simply goes on. There is no resolution, only the sense of trying again and again and coming back to the same ache.