bipolar and marriage (oil and water?)

My husband of 28 years has decided to move out of our house.  He says it is too hard to live with a bipolar but he has also sought out companionship with another woman.  This woman's husband has bipolar so they are like two kindred souls that have to live with terrible spouses.  I am so scared and I think fear made me stupid to believe that he could love me enough to stay around.  He is the major money provider of our household.  I work but do not make enough to support myself.  We have 3 sons our youngest is a senior in high school this year.  The odd thing is that my bipolar is becoming stable and all of a sudden he cannot take anymore.  My bipolar episodes consist mainly of deep, dark depressions and suicidality.  He does not want me to get a lawyer and says we can save a lot of money if we don't involve lawyers, but how do I protect myself?  I don't want to end up on food stamps.  I have my insurance, etc through my husband's job. Anyway I would appreciate any and all suggestions regarding divorce, finding a good lawyer, etc.  It is just so odd that when I finally start getting better this disease has stolen EVERYTHING from me - my confidence, my self-esteem, my friends, and now my family.  It makes me wonder why I fought so hard over the last 8 years to get stable just to lose everything.    I am sinking fast.  Dolle