Abandoning your characters for months - How do you jump back?

I think the title already explains it. I write a lot, but Im bad at finishing anything. I think the stuff I wrote two years ago is already finished but I think I still need to rewrite it. I come back to old stuff after a while, but its hard to just write anything without already thinking about what I want to end up with. Which is kind of the opposite of how I started working on the story. I already know what I want to write, so its harder to just let the story come together.