You are not responsible for him quitting his job and being broke. You are not his halfway house or mealticket.
Do you have shelters for the homeless in your town? Direct him to one of those.
This. Except, if it were me, I wouldn't even direct my ex anywhere, because that would mean I would have to interact with her. She's an adult and she will have to figure it out for herself. When we were together, I carried her burdens with her for much longer than I should have, and you can probably guess how that turned out, and how grateful she was for my support
I know this is a difficult situation, and how emotionally taxing it must be. But I implore you to think of yourself and your healing as the top priority. Remember that your ex didn't want to get back with you when he wasn't in need. I know it feels nice to be needed sometimes, but it sounds like you'll possibly break yourself (financially and emotionally) in an effort to save someone who is irresponsible, probably abusive, and will never change. I get that he has a brain injury, but that doesn't mean you are obligated to tolerate his abusive behavior forever.
There is a time and a place for compassion, and there is a time and a place to step back and let others carry their own burdens for a while. It sounds like it might be more productive if you were focus on you right now, and let him deal with his own situation in his own way. In fact, if you're concerned that he'd guilt you into rescuing him, block all forms of communication from him and call the police if he shows up at your door. These people tend to be master manipulators and have no qualms about using others to get what they want. You deserve someone who can reciprocate your love and affection, and the more time you spend dealing with your ex only delays your healing and ability to attract new men into your life when the time is right.
If there was ever a time to cut the cord, it's now. Please protect yourself, your sanity, your future. Good luck