If you've ever watched the movie 28 Days Later this quote applies to your current relationship...
"The end is extremely fvcking nigh".
Which means this is the part where if she is approached by some smooth talking playa or just a guy in general who interests her she will be engaging him in conversation and he will be in line to be your replacement as soon as she decides to cut you loose completely.
This is the way the game works.
So yeah Warrior and WC2 pretty much already laid out what you can and should do.
I think you could try pro-actively dumping her and through that see if you still mean anything to her because if you do she'll suddenly want to be in your life and be a good girlfriend to you again.
Why?
Mostly because through your act of dumping her first you invalidate her as a woman and put her in the position of chasing you instead of the way it is currently where you are practically begging for any scraps of intimacy from her that you can get.
Also what dumping her does re-establishes in her eyes you have backbone and indeed are a man after all.
All this and the invalidation of her could excite her and make her want to be with you again but if you go down this road follow Metaphysical's instructions here on it to the letter with how to mindgame her and make her work to get back in your life...
http://www.sosuave.net/forum/showthread.php?t=155594
Also be prepared that if you go the dump her approach she very well could be fine with it and happy to be free and not come back to you at all so you'd have to be cool with that if it happens.
Yeah though mostly guys who dump chicks before they can dump their guy get a good result from it so try it if you've got the balls.
Most guys these days don't have any courage whatsoever or heart so I won't be surprised if you grovel to her until she finally kicks you to the curb but yeah if that happens don't beat yourself up over it just follow our advice next time.
Any of what I, Warrior and WC2 said should work.
Thats not a diss on the other guy's advice in here btw but Warrior and WC2's posts were the only ones I decided to read before making my own post.