Hate to see you here, but welcome. There is a lot of great advice to be gotten here. It looks as though you have been contemplating leaving for a while. It takes courage to admit you have things to work on to get yourself better. I believe if my W would tell me that she has some things to work on and not put it all on me it would be easier for the both of us. Right now she is making me feel like this is all my fault and none of hers.
How do you come to the point to know where it is fear that is keeping you in a marriage? Was there a revelation? Did you figure it out through counseling? How do you know? Do you feel like once you overcome that fear, you will reconcile with him? I ask these questions because I feel like that could be the case with my sitch. While I do not have a fear of being alone, I do have a fear of not being with my W. And I believe that she has a fear of being independent. She moved out last year, but came back when she couldn't afford her apartment. She says it's because I kept asking her for another chance, and she decided for the kids to give it another try. Now she is ready to leave again but can't right now because of finances.
I am hoping to gain some insight from your sitch because I believe my wife and you are going through some of the same things and I am trying to understand so i can save my M.