Setting Boundaries

One of the things I have learned through Al-Anon and reading the life-changing book, "Codependent No More", by Melodie Beattie, is the need to set boundaries with people in my life.  Specifically,  my soon to be ex.  If I give him an inch he will take a mile.  If I talk to him about anything beyond our daughter, things will quickly escalate into an out of control mess.  It is so serious, that I have decided that I must set clear boundaries with him. I will only speak to him regarding our child and money matters.  This is all that's left of our relationship, after all.  But I find myself regressing back to old patterns of either a) bitching at him about x, y, z or b) wanting to share something about my day with him, as we used to when we were together.  I have found that doing either one of these things does nothing but open doors that should remain closed.  It is hard having a good or a bad day at work and not sharing it with him.   He's the first person I think of to tell when something significant happens in my life.  But he is no longer my confidant.  I have to break the habit of talking to him about anything other than business. Isn't it crazy that someone I once shared everything with, body and soul, is now reduced to business matters?  Has anyone else had issues establishing boundaries?