I am sorry to hear about your situation. My ex is also Bipolar II. Dealing with a person like this is absolutely exhausting, physically and emotionally. I "walked on egg shells" for years. I am now better at realizing that I am not the cause of his behavior, but it's still hard. I still do care about him.
When I left him after 17 years of marriage and 22 years together, he had been diagnosed with chronic depression for many years, but after we were divorced his diagnosis was changed to Bipolar Disorder II. He also has anger issues that he has gotten counseling for, but has not ever been physically abusive with me or our daughter, but can be verbally abusive.
I had considered leaving for several years before I finally did. What convinced me was getting counseling for myself and going through a Life Coaching program. Also, knowing that I did not want our daughter to think that this was what married life was like. He was also abusing drugs at the time and I was concerned for my daughter's safety. She was 4 1/2 when I moved out. He had lost several jobs and had been repeatedly unemployed for months at a time.
Since then he has not abused drugs, gets regular counseling and medical care, takes several medications, has gotten put on permanent disability through both the VA (he's a physically disabled vet) and Social Security. Many people who are Bipolar are on Soc Sec disability because the disorder makes being effective in a job very difficult. Not having to hold down a job has reduced my ex's stress level considerably and helped him stay stable enough to be a very good father to our daughter.
Because of the volutility of your husband's mood, I would suggest thinking through your plan and putting a plan in place before you say anything to him about leaving. I might also suggest talking with someone with experience with domestic violence prevention: http://www.ci.seatac.wa.us/index.aspx?page=263
You need support to deal with this, so please reach out to people who you trust, and people with experience dealing with this disorder. Good luck to you and your family.