I understand your shock and distress, and the pain of all that money spent without the award at the end.
But there are positives, so please help him and yourself focus on them.
Part of the value of uni genuinely is learning to live alone away from home, meeting people, testing boundaries, finding your feet. he has done that. You are supposed to make mistakes in your late teens/early twenties. It's how we all learn. Even strict Amish communities have a yera called Rumspringe where the young men go out and do all the stuff they are not allowed to do so they can return settled. So maybe, when he is ready, in a lighthearted way, ask what he has learned, not what he hasn't - everything from sorting his own rent and utilities to cooking pasta.
Unless he never turned up and failed every single module, he can transfer all the modules he passed as credits to an OU degree and top it up over time, if he wants to. Are you sure he didn;t even get a pass degree without honours. He might want to check with uni staff. It is possible to simply 'pass' without honours at a much lower level. (Or it used to be. Should be, but they don't always advertise it. Or he may have built enough credits to have passed a Cert HE in his subject if that is an option. Encourage him to check with the relevant uni staff to see what he can salvage academically from the experience.
And as some previous posters have said: loads of people thrive in the world, in highly paid jobs, without degrees.
Due to appalling circumstances, a relative of mine went from being a fully funded scholar expected to gain a first to a drop out who scraped a third. They are now the highest earner in our family of people with Firsts. Academic excellence isn't automatically much of a measure of success outside academia!
I'd want a child of mine to properly take stock of what went wrong and sort out any underlying issues such as ADHD, autism, depression, drug-taking, anxiety, processing disorders, Chronic fatigue - etc. If there was a background issue, it needs to be addressed now, at the beginning of his adult life.
But best support you can offer, alongside encouraging him to salvage what he can and sort out the reasons, is to assure him there are many roads to thriving at life and he now needs to grow up and sort out which he wants to set out on.