Giving Myself Permission to Know the Ending

So for a long time I've struggled to finish a story. I'm not sure why, but I think it has to do with how much I love to read and be surprised by the twists and turns introduced by the author. I learned early on in my novel reading career that if I was too impatient, and read the end before I had earned my way there, it ruined the story for me. (Except for Choose Your Own Adventure books. I would find the ends that I liked the most and follow the trail backwards to beginning. I hated dying in those.)
So when I began writing, I unconsciously kept the ending hidden even from myself. But that doesn't really work, because as the author, I needed to have a map of the story. Even if no one else knew what was going to happen, I HAD to, so I could lead the reader there.
So in my current WIP, I am actually writing a synopsis before I write the book itself. As if I am telling the story to myself. No dialogue, very little description except where it's necessary. I am including internal thoughts and motivations, mainly because they help spur on the plot, but also because it helps reveal character, which also drives the plot. So far I know more about this story than any others I've written. And I'm still going. I am very encouraged by this, but frightened, too. What if I get to the end of "telling", and now that I know the ending, I don't care to flesh it out?
But I'm not going to think like that. Besides, I know a few writer friends who might hurt me if I don't write it out properly. And I'm more scared of them than of the story. ;)