I have a close friend who is bipolar. Certainly it does cycle. She is rapid cycle BP II. She has also done and finished 12 cycles of shock therapy. From what I have learned, that is not taken lightly. Shock therapy is a drastic treatment that they use when other medications are not working. For her, they were really very helpful to her recovery.
I see her at times she is manic. I see her when she is depressed. I see her at times when she seems completely normal. What I don't see is that it changes from moment to moment or day to day even. Hers are normally more "blocks" of time.
So my guess is that he may be more in control at those times than he is letting on. Seems manipulative to me.
Either way, I think that she has set these boundaries and is sticking to them and working on herself and focusing on her and her DD, those are really great things. When you are around someone who is constantly very very depressed or even very very manic, it wears you out. Good for her.
I am sorry your friend is dealing with this. It's great she has a good friend like you to lean on!