Long before I asked xah to leave I knew I was done with the marriage (not that I didn't keep trying)...
How?
I knew I was done when I was lonelier having him around than I was being alone... I was so much happier when he wasn't home and so unhappy when he was and that said it all to me.
Like you we were barely roommates-- there was no effort on his part, and he was abusive though in subtle ways at first...
Whatever you decide is best for you is the right choice...