poison I really do mean this in the kindest and gentlest of ways. I think your loneliness and how this is really affecting you might be influencing how you are reading some of these replies.
It's certainly not your fault you feel sad and lonely. I don't think that's what velvetspoon was suggesting at all. I think she was trying to reassure you that you have the strength within you to change your situation. You just need some help and support to find that strength and make it happen.
I was terribly, terribly sad in my marriage. I had no friends, I was unloved, my family was small/dwindling/a joke and now there is just me. I'm finally NC with my mother; my dad died, his 'new' family didn't want to know after the funeral.
I used to cry almost daily. I used to go to bed terrified that I'd wake up tomorrow. I hated my birthdays because it made me realise that a) there was nothing to celebrate and b) just how little of my 'life' had passed and how much there was left to endure 
And now there is just me and my children. But I couldn't be happier. I'm still lonely on occasion, but without the weight of an unhappy marriage around my neck and the abject misery that brought, I was able to see the world around me. I did meet new people, I interacted differently with the people I already knew and I'm happier now than I've ever been. That's not to say I'm always 'happy', or that I never feel lonely. But it's much better than it was!
So small steps...
You've already said you want out of the marriage. You're not asking how to make it work, or how to become contented with your 'lot'. so that's the first hurdle cleared 
What comes next..? What is stopping you from saying, "fuck it!" and dumping him?