Husbands with bipolar disorder

I have a friend who thinks that her husband might have bipolar disorder. Don’t judge her for marrying and having children with him, his characteristics didn’t really present until after they had kids. Their kids are all under 5 years old. She doesn’t know what to do. There are times she wants to leave him and divorce him, but she doesn’t want her kids to have to go to be with him without her present. Like if they split up and he gets partial custody, she can’t imagine her kids being with him without her there too. So she doesn’t want to divorce him because she thinks it will be better for her to be around to be present for her children. Does that make sense? She’s never spent a day apart from her kids (neither has he). She works, he doesn’t. She hasn’t mentioned bipolar to him because she knows he won’t take it well. His mother “accused” him of being bipolar when he was younger but according to him the therapist said he was fine with normal emotions. He does not trust therapist or think that todays mental health workers are helpful. He thinks that if people have problems that they need to talk to family and friends because it’s a social problem of people not supporting each other. So she’s afraid to even mention to him that he might have bipolar because it will worsen their relationship. What should she do because I don’t know what to tell her. I see why she wants to stay. Me being a child of divorce, you never know what can happen in a custody battle. Not to mention, divorce is expensive and they are a low income family. What would you tell her? Any advice?