Viper: there's something seriously fvcked about this situation.
Think about it, for a moment. Either she's had a change of heart and decided that your relationship wasn't going anywhere (or fast enough), or it could be some sort of demented test to see if you'll admit to something (like previously mentioned, women are evil creatures). If it's the former, either speed things up or face reality and find someone else. Life goes on, and as much as you might not want to admit it, you'll find someone else. If it's the latter, well, I hear cloves of garlic and silver weapons tend to get rid of evil things.
Think about this for a moment - if you were in her position and told her you "weren't having enough fun" and just wanted to play around with another girl, she'd probably consider you a "player" and get rid of you in a moment's notice. There is a huge double-standard in relationships, but what she's doing is unnatural, maybe she's confused about the terms of the realtionship, maybe she's tired of it, who knows when it comes to women. Try having a serious, heart-to-heart talk with her and see what's going on.
I'm probably one of the least qualified to comment on this subject, but take some of my words into consideration.