Is my best friend really my friend?

[Bluelight]

Just some background info; me and this girl are best friends. Since we met, we got really close, we spend a lot of time together and I really enjoy her company. Recently though, one our of new male friends started developing a crush on her, and she was not at all interested. In fact, she was practically repulsed by him. That is, until I kissed him (he's "bi-curious"). Now she really wants him, and I already feel like I'm being displaced. I'm starting to realize how jealous she can be, it's almost like she's afraid that I'll get a boyfriend before she does, she doesn't want to be lonely. Better me than her I guess, I can handle loneliness better than her. Not to mention she's been in a few relationships, so she's not used to loneliness. But really, ouch... that kind of caught me off-guard.

I'm not really sure what to do, do I just let this run its course? I don't see any sense in forcing her to be my friend, that would be worse than being lonely. I can't even talk to her about this, she would get all defensive and stuff and we'd both end up getting hurt.