For me, JB, it took about a year of really struggling with 'is this working? Is this the person I want to be with and hopefully have kids with? Can I see myself doing this long term.?' We'd had a few pretty huge arguments before I had more or less come to the point of admitting that he wasn't ever going to change. Without going into the laundry list of issues, I should say that we had tried couples counseling (I'd been doing individual counseling for about a year and half at that point) but the crux of it was that he considered every problem to be my fault. Period. He did not perceive that he, too, had room for improvement, and that was pretty much his attitude toward everyone in his life.
We did finally have it out, basically over the fact that he wasn't helping me with any housework... but that was really more the straw that broke the camel's back. I was scrambling after that; a friend loaned me the money necessary to get me out and into my own apartment (she cited Sartre's "No Exit" as her reason for offering the loan) and I took on more hours and paid her back quickly.
Overall, I knew that no matter how hard I tried-- and believe me, I tried to make him happy, us happy, but the problem in a nutshell was that I was getting healthier in therapy and he simply wasn't. I had outgrown being the person I was when we first met and fell in love. At the beginning, I was in full caregiver mode, needing to be needed because that was what gave me value. In the end, I was healed in that area and realizing that caring for my husband in the way I had been was more like caring for a child, and really, who wants to have an intimate relationship with their son? That's sort of where the relationship ended up landing.
I'm looking out my window right now, at my little boy in a tree, eating a bit of Halloween candy and looking so proud, waving at me. JB, the best thing I could have done was to leave and not look back. Besides my sweet and wonderful husband and son, I have so much more self-respect. I feel more in charge of my life than ever before. All I can tell you is that you know when you know, and you won't know that you are there until you are there and knowing that there are no alternatives to splitting up.
I don't know if that helps, but my heart certainly goes out to you. It's a tough spot to be in.