Ask HN: Relationship with a Manic Depressive?

I've been dating my fiance for two years. She is manic depressive it seems.

Have a look at her twitter account: http://twitter.com/babymoondrop

She'll wake up one day either being a chipper as a cheer whistle, and on another being super depressed and hateful towards the world.

There is no middle. This applies to her feelings on the world, her happiness, and her feelings towards me.

Any advice? I don't think a relationship with someone like this is sustainable.