The first thing to look at in this situation is what kind of relationship you both want to be in.
It sounds like you want a sexual relationship. It appears she doesn't. That means that this isn't someone you're going to be able to have a sexual relationships with, not any time soon anyway. and not unless her feelings change. And that's not something for you to try and do: when someone doesn't want to be sexual with us, the ONLY right response is to just accept that. If WE want to be sexual with another person, we need to find someone to be sexual with who also wants to be sexual with us, you know?
have you two talked about what kind of relationship you want? And maybe, if you have been together a while, since before you were interested in a sexual relationship with her, have you talked about that it's possible your relationship might need to shift to something else, whether that's something that doesn't have to be exclusive, something that's romantic, but not sexual (and allows you to have a sexual relationship with someone else), or if maybe being girlfriend-girlfriends isn't right for you anymore if your wants are really different?
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead