As far as space goes, we all need space. I think that sometimes we can spend way too much time with someone no matter how much we love them.
As far as the ex is concerned be reasonable but don't let yourself be walked all over. Yes, I understand the concern but you don't want to be too worried about it or it may drive her away. My ex was so needy. He wanted me around all the time and I wanted to be with him alot too but there were times that I needed my space and if I wasn't with him all the time than he thought I didn't want to be with him. Needless to say it drove me away. While you shouldn't let her take you on a ride, you also shouldn't be so worried either. If she tells you not to worry about it after you've told her how you feel then maybe the best thing to do is let it go. If you keep worrying about it and pushing the subject that in itself may drive her away.
Just my thoughts.