He recently got a paper stating that he isn't eligible for his social security check no more due to being capable of working.
But, he can't work with other people because, he trips out when he doesn't do things right and Ect. way to long to write.
How could he get back on it?
Or
How could he deny their decision.

Does he have a social worker or therapist?

Yes but, he hasn't been to them in a VERY long time.

They would be the best help for him, or at least a social worker who would figure out what is going on.

What else has changed for him?

Tough economic times means fewer people paying taxes, and that means too many people living on taxpayer money, and that has resulted in more people losing things like SSI. I doubt that he will get it back, at least not easily. He will have to try to go through doctors again.

So your boyfriend hasn't seen his case worker or therapists for a long time. Its likely that, absent regular updates certifying his condition, the SSA stopped his disability. He's going to need an attorney who specializes in SS Disability to see if it can be restored.