I went through exactly what you are going through. The funny thing is I reached the point where I didn't even have to think about it. I knew, no doubts, that it was time to leave. At that point you couldn't pay me to stay.
I was still afraid and still had guilt but the doubts were gone. I had finally reached the point where the pain of leaving was less than the pain of staying.
After I left it took me almost a year before I was ready to file for divorce.
So have compassion on yourself. You'll know when it's time to leave.
Your friend,