If you’re sure that the flirting is mutual rather than just your wishful thinking, there’s a reason for her hesitancy, a reason she’s keeping you in the friend zone. Your challenge is to find a way to have a comfortable, open conversation about why she continues to flirt back but won’t take your relationship forward.
Do you discuss important life issues with her (or is conversation all just fluff)? Does she share her secrets and important personal information about herself? Have you done the same? If not, work on deepening your relationship trust and forget about what you “call” your relationship for now. Trust is critical.
Women need to feel valued as human beings—smart, funny, capable, generous, creative, hard-working, kind, talented, etc. So often young women, in particular, are valued primarily for their attractiveness. Make sure she knows what you appreciate about her. (Maybe if your mutual flirting progresses it can include touching her hand or shoulder when you talk to her, but only if it’s welcome.) As your relationship becomes more relaxed and open, you’ll be able to have a more open discussion about what is holding her back. I can think of some possibilities, but they may or may not apply to your friend:
a) she’s doesn’t want to lose your friendship if your love connection doesn’t work out
b) you’re rushing things, or she’s not ready for a dating relationship
c) something in your past dating history makes her uncomfortable (perhaps you’ve dated a friend of hers, dated a lot of girls, cheated on someone or treated them poorly, etc.)
d) she likes someone else and doesn’t know how to tell you
e) the flirting is just a fun game with you and she doesn’t mean to imply there ever will be a next step relationship-wise or sexually (OUCH – this is what you fear, isn’t it?).
Although you may fear rejection, it’s much better to know than always wonder, “What if?” We have ALL liked, been attracted to, and even loved people who haven’t felt the same way. Pursue the matter with your friend until you get an answer that either delights or disappoints, and honor her decision either way.