Post History

In my ongoing effort to weed out every beginner-related problem I might have before I write my novel (what do you mean? I'm not delaying at all), I have now come to a dreaded area: dark protagonists. 

I once wrote an answer on SE concerning dark protagonists. I said that if you provided hints and glimpses that the protagonist was not as dark as they seemed, then all would be well. The reader would be able to glimpse the light at the end of the tunnel, and continue to root for the protagonist to reach that light. 

I still believe that's a solid method. It has a problem though: it deals with a character who is not entirely dark, or who IS entirely dark, but enters the light during the course of the story. 

I am now dealing with a protagonist who starts out in the light, and falls to darkness over the course of the story. I can't very well offer the reader false hope that there's light at the end of the tunnel, because, well... there isn't. Things only get worse. 

I know that such a dark character seriously threatens the reader's desire to keep reading about said character. I am wondering what devices or strategies others might have found to help write such a character. 

Am I forced to adopt a different PoV to tell this story? Or is there some trick I can do with the character? 

Note: I'm not asking how to *change* the character. I'm purely asking how to *write* such a character so that the reader will keep reading.