@Concernemum
My sons are older and I've been through the 'less than optimum' moving out scenario a couple of times. My oldest son moved out, with no job, at 18 to take his band 'on tour' and be a 'rock god'. If you don't think I was absolutely frantic, you're dead wrong. But after one 'Are you sure?' I kept my mouth shut and pasted a smile on my face. He 'got it out of his system' after 6 years, got a job 'in the industry' and is now married and doing extremely well.
My younger son is now contemplating taking a job (in his profession) about 100 miles away in a more expensive area AND with a car that's on its last legs. I'm keeping my mouth shut about how thoroughly he's checked out living costs there and what would he do if his car gives up the ghost.
Here's my advice:
First off, do not offer money. He wants to and needs to 'sink or swim' on his own. BUT, silently put what money you can afford in a savings account and let it build up. Then IF the time comes that he wants or needs to come home you'll have a tidy sum to pay for his airfare/travel needs. Just don't tell him you're doing this. I did this with both my sons. That money is still sitting in a bank account.
Secondly, stop asking questions, offering your opinions, or making suggestions unless you are specifically asked. Yes, you may be older and wiser but he's not listening anyway and the more you talk the thicker that brick wall you're speaking to becomes. So save your breath to cool your porridge. If you want him to come home in the future, don't alienate him now.
Thirdly, since this appears to be affecting you emotionally so deeply, you may want to consider counseling. If you don't want to completely alienate your son or make him feel as if he can't contact you should he need to, then you need to find another outlet for your fear and anxiety.