When you are making a decision to leave or stay don't think about how it is going to affect him. He's in charge of that.
Really - what is in your best interest? Do that.
That seemed unimaginable to me at one time but it is how I try live my life today. I had spent 16 years with my husband. There were even some good memories. My martyrdom, my sacrifice, meddling, trying to control outcomes, trying to run his life, manage his emotions, protect him, whatever it was I was trying to do....led him/us straight into the hell we were living. Really, I wasn't doing him any favors so who did I think I was?
I decided it was kind of wrong thinking to believe that my leaving was going to devastate him. He was already pretty devastated from what I could tell. He was not going to see it that way (and may never) but that is just the way it is.