My strong suggestion: don't let him move in. Please don't.

You need and deserve your own space and life. You can be a great role model to him by doing so.

He needs to get financially stable. If that means he needs to crash on someone's couch (not yours) and work away at a low wage job - so be it. He needs to build himself up.

You deserve an adult boyfriend who can take care of himself. Maybe eventually he can do this, maybe not.

He also needs to untangle completely from his ex. That is if he wants to be in a full adult relationship with you.

He needs a job, he needs to find a job and keep it. If there are other things going on mental health wise then he needs to go through the experience of not succeeding in the work place, being properly diagnosed, and then maybe apply for something like SSI.

Unfortunately if you let him move in you are sacrificing yourself and not helping him any at all in the long run. And once a person moves in it can be difficult to get them to move out, no matter what they say initially.

I really feel for you in this situation and wish you well, sounds like you have a good head on your shoulders and you know what is best.