I think what you're wondering about
is why BP sufferers are inconsistent. And that is unanswerable, scottyteal. I wish I could tell you. You're looking for an answer rooted in brain chemistry, social history, how insecure a person may be, what their parents treated them like... Yes, depressive/manic cycles may have something to do with it, but it may be the reverse too. Some people have affairs when they're manic. I'd say you're being simplistic, because not everyone has the same problem you're having. Some of us don't break with our partners at all.
As has been suggested -- some of this is BP, some of this is just who your girlfriend is and it has nothing to do with her BP. Of course she craves your safety and stability. And she is afraid of making herself vulnerable too, probably -- she has a disorder which makes her very unpredictable, and vulnerable, even to herself.
I'm sorry I can't offer more concrete solutions for you. I can only suggest you be firm and consistent yourself, because I can tell you that's something many BP's crave and need themselves. What do you need? Take care of yourself, making as much room for her as possible, and she'll either follow suit or not.
SerafenaCo-Moderator, Bipolar Forum