Oh ImpossibleBlonde I feel for you, so much 
First of all, I'm not surprised that your husband is the way he is when he was, presumably, brought up by this woman.
Just a few thoughts - you say if you leave, you will have no friends - do you have any now who are really there for you and helping your dreadful situation? Likewise for social life etc.
If you can even start to get some life for yourself, you can eventually make proper friends of your own and a social life too - there are plenty of opportunities unless you live in the back of beyond.
But what you need first of all is a rest. Please see your GP as a first step and try to get some respite.
It seems to me that your husband and his mother have managed to convince you that your only worth is through serving them. This is obviously not true - not for anyone - but if you cannot see it, don't blame yourself. You are not getting enough sleep, time for yourself (yes, there is such a thing and you are allowed it!) or support (which we all need, especially in such stressful circumstances).
I don't think anyone would expect you to just walk out, with nowhere to go, but what will happen to your mil if /when you are hospitalised?
Leaving or even changing things is massive, I know, so try to break it down into small steps.
What can you do first? What will help?