Should I ask her out?

Right, this is a bit of a tricky question. I have a really close circle of friends that includes roughly 12 people, but there’s this one friend that I’ve developed sort of an attraction to, if you know what I mean. She’s gay, and I’ve always thought of myself as straight. I don’t feel the same way about her as I have with guys I’ve liked, but it’s definateley different from how I feel about all my other friends. I asked her once before, just in general conversation, if she’d date me if I was gay, and she said yes. So now I don’t know what to do. I read once that while you’re young you should just presume you’re bi and date whoever feels right, so should I ask her out? I’m not only fearing rejection here, but also if she says yes,and I decide I don’t like girls after all, and it’s just a “phase” or something like that, she’ll be sad. Also, if we go go out, but we break up, it’ll be really awkward for both us and the rest of the group. So, any advice?