actually, I really understand being scared of caving, after I made the decision to leave xah I was very scared that I would be talked round again, as I had been before. For me that fear wasn't based on my not being ready, it was based on self-knowledge and the evidence of my past behaviour.
the fear that I might chicken out, didn't stop me, it helped me rally and build resources (a therapist etc) to help me work through that. I am now more than 2 and a half years on from that decision, divorced, and have bought my own home. there have been times when it has been really tough but never anywhere near as tough as living with an active alcoholic, and I have never regretted leaving for a second, although I have mourned the fact that leaving was my best available choice. I no longer regret those times I caved before, because I knew when I left that I had done everything in my power to save the relationship, to live with it, and been beyond reasonable giving thousnads of "last chances", but if I had my time over I would leave earlier.
Use the fear, see what it tells you about yourself, and marshall some resources to help you work through any issues it throws up during the process.
xxx