Welcome to PC! You'll get great help here, everyone cares about each other and tries to help to the best of their ability, I know PC has helped me through a lot in the past year.
-I think I can relate to your situation. Because I am 'the bipolar girlfriend'.
My name is Kaci, I'm 16 years old, and my boyfriend is 20. (Which that sounds bad, but if you knew us , it's really not. But that's a story for another time.)
During this past year, my boyfriend has brought it to my attention that I have many symptoms of Bipolar Disorder and Depression. , and like you said about your girlfriend, I'm too stubborn to get help. I did however, join this site and it helps a lot. This site actually convinced me to tell my mother everything.(which I did) , but I have yet to see a doctor.
Anyways, I too, go through those 'downspirals' and want next to nothing to do with my boyfriend. , it has caused a few break ups and many fights over the past two years. (mainly at first, because we didn't know it was bipolar that made me that way) but, we've somewhat learned how to handle it better ( don't get me wrong, we're a work in progress. ) -I'm just trying to say, if you don't give up and you really work at it, I know you two can make it. , It's not easy, and it's never gonna be easy. But you have to make the decision and decide whether she's worth it or not.
..I just realized that I'm writing a lot (I have a bad habit of getting off topic) , but I just wanted to let you know that if you ever need someone to talk to, or have questions about what to do, or what something means, feel free to talk to me, I'll always be here to help.