I suspect camping cot may be a “poor me” ploy to get you to let him stay. Sounds like it had some effect perhaps?
He has a safe place to go and apparently enough money to take care of himself.
He has to choose to make changes that last— it isn’t your responsibility.
If you can shift the focus back on yourself and your needs you will find peace much quicker.
It isn’t easy to see someone we care about continuing to make poor choices, but he an adult and entitled to live his life as he chooses.
That doesn’t mean you have to have a front row seat— I strongly suggest going no contact, at least for a few months, after he leaves to let things settle and get your balance fully back.