I can understand your gf's frustration.
There is so much literature out there to educate normals how to deal with us "special needs" folk but none of it schooling us on how to deal with them.

What I have learned in my own life and from trusted friends here?

Don't treat normals as a crutch, you're not broken don't expect them to fix you.

Don't be bipolar 24/7 (bear with me);
When your dx is the centre of your universe and your world revolves around moods and episodes, you are subjecting others to that reality too. All they end up seeing is your dx, and in this case it wouldn't be their fault.

When you're inbetween episodes, enjoy it, dont fret about the next one. This gives you time to breath and the SO time to relax and see you, instead of one or both of you waiting for the other shoe to drop.

Don't be a coward and blame bp for bad behaviour.
Own your shyt.

Don't involve SO's in everything bp related, you'll wear them down. (me, my bp and bf stays seperate atleast while we are still living seperately, I may reconsider in the future).

Don't put the burden of understanding bp on normals. They can't and they won't no matter how they try. If they say they do, they're lying. Literature can describe the disorder, but it cannot relay the bipolar experience. Instead aim for acceptance.
Acceptance is a worthy goal, to be accepted worts and all, without the ability of understanding speaks volumes and also places MUCH less pressure on the normal in question.

In essence, bring more than bipolar to the table. Many of us get so caught up with wanting people to be supportive and needing them to put up with our shyt, desperately seeking understanding, that we forget we need to have something to offer too.