I believe that if you don't want to spend the rest of your life with this person any more then you should explain that to him, divorce, and move on.
I completely agree that you shouldn't have to justify yourself to anybody else, but you obviously need to tell them something. I would simply tell them the truth, explain how you feel in the simplest way possible. If they don't understand then there is little you can do about it.
I broke up my first marriage because my husband was abusive and I realised that I didn't like him or need him in my life any more. Not really the same thing, but relevant. As soon as I ended my marriage, I discovered so many things I had been missing out on. Don't hold yourself back by staying in a relationship that's not right for you, get out there and discover the things YOU have been missing out on. You never know, you might meet another guy who is as awake as you are.
Hopefully your husband will also move on and find something he was missing out on as well. Good luck to you both.