It does sound more deep seated than simple loss of interest. As Michelle as mentioned, it seems to me that the aversion to being touched could be related to abuse or neglect at some other point in her life (even as far back as birth and early infancy). Why I suggested starting with holding hands is because it is innocent and non-threatening - most people can tolerate being touched on the hand or arm even if they don't like being touched. So it might be a gradual way of re-establishing some contact.

I definitely think counselling is the way to go, as this is probably too deep for the two of you to try and work out on your own. It sounds like it is going to take some time, so this is why it would be a good idea to get your own mind into a state where you understand and appreciate why it is worth it to you and how much effort you're willing to put into it (your wife's counselling/your marriage). If you can keep yourself focused on the end goal of having a healthy, happy wife (rather than focusing on the negative of not having a sex life) you might find it easier to stay steady through the process ahead.

I'm wishing you both the best. I hope you can find some way to help her without it causing financial strain.

Craig-I feel that there is a lot more information than is being said in your posts. There is a deep-rooted problem and if it has been going on for over five years, something has got to be done.

Do you know nothing at all about your wife's childhood, teen years, abuse if any? Is there illness, mental or physical, that hasn't been addressed? Was she raised in a very strict, religious family that taught her that sex was evil? When you were dating, what was her family like? Come on Craig, there are answers to these questions here somewhere!

You mentioned "not wanting to leave your special needs child in her mother's sole custody." Why? Are you afraid she will somehow harm the child?

Divorce is only an option and a last resort at that. But listen, Craig, fifty is not old at all. You are sacrificing your life for your children and you are truly not living. Children grow up and have lives of their own. Your life is too precious to waste. Are you really willing to go through the REST of your life miserable? No marriage vow is worth that.

Get your wife to a doctor as soon as possible. Unless you want to be miserable, it is the only thing you can do. Force the issue.
We were put here to be happy.