Hi Gb66, glad you found us too!
I haven't made this type of decision, but when I read your post the first reaction I had is - you look after yourself first. This is such an important thing because, as I'm sure you know, if you are not, you won't have anything to give anyone else. You are in a high stress situation and it's imperative that you put yourself first.
I'm sorry your daughter is going through such a rough time.
All children would like their parents to stay together (generally) unless the situation has gotten to the point where the environment is so emotionally draining it just can't go on like it is.
I had an alcoholic Father, yes, he was functioning too, not really as a Father but as a provider. My parents eventually divorced when I was about 17. I never liked them as a couple however I understood why my Mother stayed (financially). Children of alcoholics don't feel safe (generally). I was lucky, as are your children, to have a Mother that was stable and great and caring. But in that type of situation there is always that tension, always dysfunction, always something. So while your Daughter might find some kind of comfort in the "sameness" of home, you know it can't go on like that, for you.
I think, in your case, I would suggest getting professional help. Perhaps you can speak with a therapist that specializes in bipolar, to help you to find a good and safe way to speak to your Daughter about potentially leaving your AH.