I agree with other suggestions. You need an attorney. Do all of your homework and planning, don't tell him anything or let on. I only told my ex- the day after my attorney filed the divorce papers. She made a new will for me; power of attorney to my sister, etc.
You are entitled to half of the joint funds. I moved funds into an account in just my name right before I told him that I was filing. Start putting away some cash. I would get cash back every time I went to the grocery store.
Remove your personal valuables, make copies of all financial documents,
make sure you have everything set up for yourself, then file and then tell him.