Erm!! maybe being to up front and honest that you'd liked her for ages wasn't a smooth move.
Basically you rushed into it to much and she has backed off. Maybe take things slower. Just chill out with her and be the friend she wants you to be. Then as she becomes more comfortable with you then things maybe will work out.
I second that. I've found the longest relationships lasted because I wasn't trying to impress her. It's a lot easier to be yourself when you're not making a point to chase her. Have fun, and if there's something there, it'll come with time. She may not be the one either, so just because you're not dating doesn't mean you can't learn.
Before my current fiancee, I was engaged before, and that went to pot. Better an ex-girlfriend than an ex-wife, I say. However, I learned the difference between having a female friend and having a partner for life. There's a major difference, and if you go too fast, you'll push her away or end up with a broken relationship---and those suck, no matter how amicable.
In short, slow down and be yourself.
Women think differently, and what we ogrish men might think is okay might be entirely off-putting to her. If you're up for some reading, pick up some books for pre-maritial couseling, like
Men Are From Mars, Women Are From Venus. I know marriage isn't in the immediate forcast, but the insight into why you think the way you do and how it relates to her is worth the read.
In a general sense these help, but you'll have to spend time with her to make it work out.