What should I do? I think my husband is bipolor or worse?

After struggling for 5 years in my marriage, I found out some vital information this morning about my husband. He has mood swings. In the mornings, he usually starts the day out very energetic and manic. He is usually happier at these times. However, once the sun goes down, he turns into another person. He becomes, mean, cruel and sometimes psychotic. He has NEVER cuddled with me at night time ( I am a cuddler like most women), but it is as if he HATES the human touch. It really hurts my feelings. Anyway, last night, we had a huge fight. It came out of nowhere. He told me that he had a bad day at work. That's all I know. Next thing I know, he is calling me disgusting names, and saying horrible things that I will never forgive. His sister happened to be at my house this morning. She knew something was wrong and I told her the truth. She admitted to me that something was mentally wrong with him and that he needed to be on medication. She was very kind and understanding. I very much appreciated her honesty as this is the first time my suspicions were validated. Anyway, she said their other brother was DX bipolar and that she thinks he is too. I know something is wrong with my husband. What should I do? I don't think he will EVER take medication. Can this marriage survive? If he miraculously agrees to get help and take meds, do we have a chance or does this have to end in divorce? I am devastated and feel our marriage won't stand a chance now that I know he is mentally ill and untreated. Please help! :(