Thanks everyone! Especially Jim, I'm looking up codependency and I definitely think it describes me in general. I do think, however that I tend to overanalyze, but in this case I'm just trying to get to the bottom of this relationship and find out whether it's worth preserving at some level.
I think she may be worth keeping at some level, as we grew up together, but maybe only as a friend in a very casual sense of the word. As in acquaintance, whom I happen to know a lot about. I'm gonna say no to future requests that make me uncomfortable, and just try to put less importance on our relationship in general. And if she crosses a line, I'll let her know.