The thing is OP, has he actually ASKED you for help, or are you just assuming the worst and panicking? If he's asked for help, the only way you should really help him is by pointing him in the right direction to get assistance with things, ie, if he says I haven't been paying the mortgage, and I've had a letter saying that if I don't pay they're going to repossess my flat, what should I do? Then you can suggest that he contacts his mortgage people, and tells them his situation, and asks them if they can help him. Whatever you do, don't offer to pay it for him. You can also point out that he would be able to pay the mortgage if he weren't being so fussy about what jobs he wants to do, and that if things are this desperate he needs to get a job, ANY job, and quickly. However, the last thing you should do is encourage him to move back in with you, as he will then end up staying until you die. Sorry to be so blunt OP, but you've basically admitted that you've made a rod for your own back, so if you want to put a stop to doing everything, for everyone, you have to reign yourself in, and let people sort their own problems out, otherwise they never learn.
My DM used to sort everything out for my eldest DS, but was happy to leave myself and my other sibling to our own devices, as we weren't as feckless with money as this DS. We kept telling her that while she did this, she would never learn to stand on her own two feet, but Mum carried on bailing her out until the day she died, all the time worrying that my DS would lose her house if she didn't. Mum has been gone for 22 years now, and amazingly, my DS still has her house!!
Read my last paragraph again and think about it!