Like cmc, I have been where you are and I remember the painful indecision. I knew what was right but I was too scared to do it, I lived 24 hours a day in that dark place called "fear".
I could encourage you to do things differently than I did, but the truth is, I think you have to do what you have to do and when you hit an "enough" point, it will be easier (but don't kid yourself, it won't be totally easy).
I had the nightmares for years too and spent my days exhausted from very little sleep. Be careful of that, it will affect your physical and mental health.
What helped me most, during those times and after my son left, was going to meetings and learning to work the 12 steps that saved my life. I will encourage that, if you don't already go, because I know it will help you more than you can imagine.
So today I am sending very little advice, just a bucket of hugs because I know how much you need them. And some prayers too, God's used to my daily list
Hugs