Your story is so similar to mine, except for the miscarriage part. I had been dating a girl whom a suspected to be bipolar as well. We went together for over a year and a half and although we had some really good times and really cared for one another, it was just too hard on me to continue with the relationship. I broke up with her a few months ago after a string of manic and depressive episodes.
I never knew who I was going to be talking to each time I saw her. One day she could be extremely happy and joyfull, and the next something would trigger her and she wouldn't want to see me or anyone else. I was verbally abused so often that it began to have negative effects on my mood as well. She always had a complaint about someone. Everyone, it seemed, ticked her off for some reason. Whenever she was upset, it was always because of someone else.
She refused to see a professional due to the costs involved. Her up's and down's eroded our relationship from the second month we were together until the end. I tried explaining to her that until she received help, each relationship she entered would have the same result. I am actually fearfull she will end up with an physically abusive person because I just don't see how a nice one would ever want to stay with her and accept the abuse she gives.
Even though I could never get back together with her, I still really care for her and hope she can get the help she needs. I fear she may do something to hurt herself some day or be hurt by someone else.
From what I understand about this condition, it never really goes away. Medication and therapy can mask or suppress it, bit it will always be there waiting to resurface. I would advise you to just leave the relationship and be glad you didn't have a child with her. Staying with her has the potential of seriously damaging your own life. Just my opinion from my own experience.