You aren't utterly lonely, it just feels like you are, and being lonely in company is probably just as bad as being lonely alone.
I do things like come on here, go for a walk, go to buy a newspaper or something, just for some human company.
One thing you could do, is do those things, or maybe go to gym class or for a run, for some genuine alone time. Your husband can mind the DC for an hour or two.
It sounds counterintuitive, but amateur psychologist that I am I think that you are losing your identity - you're Mum or The Wife not Fortunate , so that's why I'm suggesting you get a teensy bit of headspoace.
It sounds like your marriage is on it's last gasps. Would there be any point in counselling as a couple?
If you could describe how you would like your life to be, what would it be like?