@TerfBangs..... I'm glad that you are planning to leave him. It's imperative that you do. But let's look at your fears:
I am so scared of separating though. The financial strain, the effect on our son. Potentially depriving him of a sibling.
Of course you are scared. You were a child when you became a couple. In many ways you still are, because you never got a chance to learn to be YOU. Yes, the financial implications are daunting, but you simply have to find a way, and you will. You are a grown woman and you can do this. Being poor as the proverbial churchmouse will be better than the sham of a life you are leading now. And that applies to both you and your child. Forget about him being deprived of a sibling. No, just no - don't even think of bringing another child into your toxic marriage. What your son is currently learning about relationships is seriously detrimental to his psychological wellbeing. Think about that.
Being alone for the first time in over a decade. Then possibly dating as a single mum. My life has been so orderly and progressed in such a linear way I just can't believe I'm about to blow it all up over something so ephemeral as not feeling desired.
You know perfectly well that this is not just about not feeling desired. Your husband, for whatever reasons, is totally cold. He literally does not see you. He is a sad excuse for a man and he will not change. Whatever his issues are, they are his to fix, but he wont, because the status quo works for him. Why? Who knows. His childhood probably. But the reasons don't matter. You cannot fix him, and he is not yours to fix. He has chosen not to care that you are deeply unhappy. Every day he knows that you his behaviour is eating away at your soul, but he CHOOSES not to care.
Your life has been too orderly up until now. So orderly that you have been able to suppress all the normal aspirations and emotional needs that drive people to create a life for themselves that has meaning.
Forget about dating - first you need to become YOU, which means being by yourself and doing the work you need to do to learn the things you should have learnt 10 years ago. Being alone without being lonely, having self-esteem, doing what what you need to do instead of taking the 'easy' road, building and treasuring relationships that enrich your life. It is never too late, and you should actually relish this challenge, because it will be a far more interesting journey than to continue drifting through life in quiet despair.
Sorry this is long, but I feel very sad for you. You deserve so much better. I'll leave you with my go-to motto and a couple of suggestions of books that you must read.
Tell me, what is it you plan to do with your one wild and precious life? (Mary Oliver)
Women Who Love Too Much by Robin Norwood
The Six Pillars of Self-Esteem by Nathaniel Barden