I think most people have been in debt, at one point I was £26k in debt on credit cards with nothing to show for it....
The first positive step you have made is opening the letters. It is so so hard to do, and takes so much strength to see in writing how much you owe. But now you know.
The next step is working out how to deal with it.
Your OH needs to get a job. Any job. ANY job. I cannot believe he hasn't in all this time?!
How old are your children? Does he look after them in the day? If he does he can work in the evenings and weekends. If he doesn't he can work day and night if he needs to.
Why has he not worked for all this time while you're both getting in so much debt?
The next step is to write down who you owe what to, call them and explain what's going on. They will want to try and help. They want to try and get their money back if they can, so will try and help you come up with a solution.
Go and see the CAB, speak to someone and get their advice. Speak to some of the suggestions other posters have made.
The last resort could be bankruptcy. It's not an easy option at all, and will bugger up your credit for the next 5-6 years, BUT it is an option.
Please don't do anything bad, and don't think sex work is a way out, it isn't. There IS another way, you just need to pick up the phone and make some steps to change things.
You can do this, you will do it for your children.