This is a tough situation. The normal PUA response to this situation is "move on." Personally, I hate that "advice," is nothing worth fighting for? Now the question you need to ask yourself is "is it worth it?" If there is something about one girl that just has you going crazy for her and you want her as a gf because being a friend just isn't enough, give it a shot. If you just want to tap it, I'd really just stick to the relationship you've got now. That friendship will be ultra valuable in getting a lot of pussy.
Now if you are in that first situation then I got your back. First off, the key is to use good kino. She's already comfortable w you so it'll be easier to escalate, do it right though you just want to establish yourself as a sexual being. Now have you ever broken up a bf/gf relationship? Because its basically the same idea. You're breaking one relationship (friendship) to start a new one (bf/gf) so the same rules apply. So here is what you do:
1. Keep gaming other women in front of her and never talk to her about your game again just that you got a girl and the stuff you did once you got her

. Make sure she knows you've got other options.
2. Start saying what a bad friend you are but what a great bf you are. You have to break the idea that keeping your friendship is more important than complicating it with deeper emotions.
3. Start planting in her head all these amazing things you'd do if you were together. Example: "Oh yea we are going to go backpacking through Europe. We're going to have tea with Prince Harry, go bungee jumping off the Eiffel Tower, sleep under the stars in Rome, and go skinny dipping in the Nile River. That's just for me and my gf (even though you don't have one), sorry, you can't come.
4. Spend more time with just her and escalate your physical relationship in private. Find dumb ways to make her kiss you, dance dirty with her at clubs, etc
5. Finally look for the signs. Look at her repsonses and make a judgment at whether she is interested.
These 5 steps have worked for me twice (the first time w/o me even knowing it). I'm also working on another difficult situation with a girl who is a new "friend" but also has a bf, so its a double challenge but I'm already making progress. Good luck my friend hope it helps.