This is hard.
Girls are able to develop very close, strong, trusting and deep relationships -- minus the sex. I have two friends that I text all the time and hang out with all the time and that I can honestly say I love... minus a sexual attraction.
If she confessed to you that she's bi curious it was probably because she was encouraged by your confession of your crush. Its flattering and interesting and she wanted to share with you.
My money is on that she told you she had unsure feelings for you because
1.) She's confused about her sexuality, and
2.) She trusts you enough to guide her through this, but
3.) Is NOT willing to risk your relationship if the answer is, "Gee... I guess I really do like boys after all."
You should support her decision to explore as a friend, and if she turns out to truly like both sexes, than that may open up for a serious relationship down the line. But right now, she's too confused to enter into a relationship with anyone.