So much going on in your thread, Pup. Everyone has their own view. I see it as more complex. Each issue brought up is relevant, but the big picture is complex.
Your W's and your needs are not met. In order to get them met, changes will need to be made. What changes? That's what you and your wife, and any helpful counselors can figure out. Make a plan, TOGETHER, and follow through. If she doesn't follow through, you get to the end of the week, call her on that, figure out why, and go to the next week.
I've heard people mention cognitive behavior therapy on here. I believe, it's basically doing what I mentioned up above with a counselor. If I went back to counseling, that's what I would do. It's action based rather than just dumping all of your problems verbally on the counselor and talking about childhood. I found I got nowhere fast with that approach.
It seems as if writing works for both of you, too. You could dialogue journal with her, like in Retrouvaille, about specific issues as well. She reached out to you in the letter and shared her fears. Maybe if she feels you could understand them...just understand them...that will be half of the issue right there. NOt to mention, she would need to understand YOU as well when she reads what you wrote. Perhaps, just getting down and dirty and assertive sexually would be all it took, but I don't see that as being comfortable to you in all ways. So, there needs to be some talk about it. Maybe the dialoguing wouldn't be helpful for her up front, but maybe it would be for you, and then in the end for her.
Those are just a few ideas. You're like my H and I, though, in that it just seems like a whole lotta work and a whole lotta the same thing, and bottom line you just have to start DOING something. But, unless each of you figure out WHAT do do, you can't start doing it.
As always, trust in God. God hates divorce. Your W is the woman you should be married to. Figure this out. Don't give up.