If you want to write stories, why not do so with me? I'm the same way. I have tons of ideas for stories, but I only ever get a little ways in before I quit. But if I RP, or write collaboratively, I tend to excel at it.
Actually, I have a tiny smidge of fanfic... (really, it's only a page with some notes on the bottom), if you want to see what I write like (though you already have an idea through the RPs.)
If you're interested, I'd love to write a story with you.