I like this girl, but she doesn't understand I need more space than most. How to tell her?

Just tell her how you feel. Since you are a writer you must have a way with words. My brother is exactly the way you are and I'm very concerned that he may end up lonely too. I know from experience that when it comes to relationships you have to sacrifice some of your small qualities. But I know that in your case it isn't easy to change, but you are going to have to learn how to let your guard down. One thing I would do is find out about her past. I'm sure you don't want a fast girl that has done wrong in the past. Before you let your guard completely down make sure she won't hurt you. If she's dated a lot of men and had lots of boyfriends then she might not have the patience for you. I would hate for you to live and die alone all because you had one chance at a girl and she ruined it for the rest of them. Because of your cirstances, when you find a girl, you have to make sure that they truly deserve to be with you.