So classic oneitis story, you've been LJBFed, go game other women, etc.
One thing that worked for me purely by accident, and then afterwards I checked out Adam Lyons' little graphic about it [youtube]
http://www.youtube.com/watch?v=r9jeyLvpuBM[/youtube] which explained what I had (unintentionally) done is this:
Basically if you create too much comfort without a rapport break, or without any kino escalation, then you get friended pretty quickly. The only way to break out of this is to go very far the other way, and basically take things super sexual to the point where you may risk losing the friendship (I would add that to start out you do a massive rapport break too, i.e. a 2-3 day freeze-out).
My situation was like this. I have a female friend who's one of my best friends from my first year of law school. During that time she had a boyfriend and I had a bunch of MLTRs. It was clear that we got on well and I know I'm her type because her boyfriend looks scarily like me and has a lot of the same interests. I don't game girls with boyfriends because to me the point of all of this is to make yourself a better person and make everyone around you happier, and trying to steal girls away from their boyfriends is fucking shitty. So we have remained good friends.
I hadn't seen her in a while (seems like a month or two's freeze out), then when I met her I was super excited to tell her about all these adventures I'd had, and a series of stories involving multiple girls. This obviously had the effect, after not having seen me in a while, of spiking the attraction levels tremendously, and also creating a certain amount of jealousy (if he's going around with all these women how come he's not hitting on ME?) So I swung the interaction meter over to "player" from "safe, comforting friend." She initiated some friendly kino, which I reacted automatically to, without thinking, by escalating slightly then pushing away. Long story short when I went to kiss her on the cheeks goodbye later in the evening she pulled me in for a proper kiss, which I was totally not expecting (but I'll take any day of the week!) Since I was actually leaving and another one of our friends was RIGHT THERE, and she still has this boyfriend, there's nothing I could or wanted to do to take things further. She texted me the next day saying "crazy night...don't remember anything after 10pm!" Which is conveniently specific because I said goodbye at about 10:30!
Point of this story is, if you have a friend and you want to get out of LJBF mode, you firstly want to risk losing the friendship. Secondly, game other women so you have true stories to tell about your exploits (and also maybe you'll realise how non-special this girl really is). Thirdly, freeze her out a while. Fourth, meet up with her and re-ignite your attraction levels by being in an environment full of cool friends, girls, where you are a leader. Tell her stories about other women in your life, be the centre of attention for some other women during that time, and so on. Then initiate friendly kino and start escalating using push-pull whilst re-building comfort and hitting those commonalities that made you friends in the first place.