First it all, it sounds like you're trying to convince yourself you should have a physical relationship with her. She doesn't have to be "the one", but don't get so fixated on one woman. If you settle just because she happens to be the only girl you talk to and you get married for that reason, you'll regret it later. I know from experience
That said, as others have mentioned, you're basically dating her already. If you want to fuck her, man up about it.
I'm so fcuking tired of hearing about the "Friendzone". Friendzone guys are just guys who are right on paper, but are needy, dishonest about their true intentions, and don't man up and put their own priorities first. Those qualities are very unattractive to a woman. Manning up/growing some balls means you're willing to put yourself in a vulnerable position and take a risk.
Ask yourself what you really want from this woman and why. If you want to be buds, be buds, but make sure you spend time improving yourself and find women you want to be friends AND lovers with. If you spend all your time with her, that won't happen. In fact, if she really is just buddy materiel, talk about other girls with her...maybe even ask her for advice. If you want to get her in the sack, start getting physical with her, and DO IT UNAPOLOGETICALLY. It's difficult at first, but the only way to become comfortable with it is to get out there and do it. It's a vulnerable and uncomfortable place to be, but taking risks like that is what makes you a man.
You also need to change your views on rejection. Rejection can be a good thing- it prevents you from wasting your valuable youth on women you aren't right for. If she shoots you down, don't apologize for it. In fact, it might just be some token resistance. You can keep escalating while saying "oh...yes...we shouldn't be doing this". Or, if she makes some logical points that you actually agree with, then just agree with them and say "yeah...I suppose you're right, we are better as friends". Just don't apologize. Continue on the next day as though nothing happened, because it REALLY ISN'T THAT BIG OF A DEAL. Then be very blunt talking to her about other women. She'll either help you out, or get jealous and make the moves on you. Win/win.
Also, do yourself a favor and buy this book...
Models: attracting women through honesty by Mark Manson
The author has a great blog and podcast, too called "Postmasculine"
It'll be the best $15 you ever spent.
I also recommend you search YouTube for Richard La Ruina, Sasha "Daygame" and James Marshall. They'll show you how to be a man who gets what he wants. Their info isn't as good as Mark Manson's though.