I'm not a girl expert, but with me it usually means she isn't interested, and is letting you down easily.

It may mean that she doesn't want a relationship but you never know, she just be out of a bad one or something. And she wouldn't want to tell you because she wouldn't want to hurt your feelings.

I think you should ask her to get things sorted :]

You're old enough, and she's probably old enough... for that expression to mean she doesn't want to be bound down to any commitments. You'll find this frequently if you are approaching or currently in senior year of high school or college. But if she likes you, and she meant it when she told you, try getting with her or something, work on a physical relationship and it may eventually turn into something more. If not, you got some pleasure out of it. That's about all you can do. Don't waste your time trying to change her mind.

^ yeah thats the reason I used to use that excuse, and also at the time I had school work ect and I really couldn't commit to it.

Relationships are so demanding and damn annoying sometimes, need space

The more you try to change it the longer she'll take in my opinion Just stay being friends for now, in the future maybe, doesn't necessarily mean she doesn't want one with you, it's she might just have more "important" things to focus on at the moment.