OP, first of all, I’m sorry you’re so unwell and I hope you will recover. 🌺
Secondly, don’t take the nasty comments on here to heart, perhaps some people didn’t quite understand what you meant and also they missed the fact that you would have been able to work and pay the loan back if you didn’t get sick.
Your only ‘mistake’ in my view was initially agreeing that your son could live with you rent free (or for a low rent without a firm agreement), thus giving him a feeling of entitlement. But ok, you did that to help him and did not know your financial situation was going to deteriorate. But he does owe you £300 per month from the moment you both agreed that this is what he should pay you for rent. So multiply that by the number of months since you made the agreement and take the total off the £20k debt.
Then do another, more realistic, calculation going forward - how much rent would it be reasonable for him to pay you, plus bills, plus food. In my view this would be significantly more than £300 per month. If he doesn’t agree to paying this kick him out and get a lodger. The lodger would pay you more than £400 per month (esp if you include money saved on not buying son’s food) so this would enable you to pay the loan instalments and also give your son some money owed for previous loan instalments.
Your son is 25, he is an adult and he earns good money (presumably because he has a good job which he partly secured because he went to a good private school which you paid for). I have little sympathy for him. Yes, you agreed to pay the loan and then couldn’t, but that’s because of reasons beyond your control. He is in effect an unsecured creditor and if he was to take the ‘legal’ option and take you to court he’d get a court judgment asking you to pay only what you can afford based on your financial statement .
My brothers were awful to my mum until she died from cancer and I will never ever forgive them. This post triggered me.
so sorry OP