"Dark" seems to be the theme of this song. I think that the dark means harsh times of struggle.
Picture yourself in a forest in the pitch black dark of night. There is one small light, always moving and going somewhere, and wherever it shines is the only place you can see, with nowhere else to go, you follow the light. The light that has been guiding you just extinguished, and now it's dark all around, you need that light to go anywhere, otherwise you're stuck in the dark, can't see to go on.
As I said, the dark means harsh times, and the only hope for him is that one person being spoken to in the song, they are the light. When that person stops guiding and helping him, there is no hope for him. Now they are gone, there is only darkness (harsh times of strife) nothing more, and no matter what direction he goes, it's still dark all the same.