Have him swap his emergency contacts from you to his ex.

Nope not a typo. If he wants to be with his ex but doesn't want treatment that's on him. They should not be calling you to make you worry about his health or panic. You aren't his caretaker.

Re: caretaker firing. His girlfriend doesn't have that power so that was his decision in the end.

The only thing you can do at this point is contact adult protective services, social workers or 911. If he refuses to remove you from emergency contacts then every time he misses an appointment give the non-emergency 911 number a ring. He's an amputee and can't drive and his girlfriend could absolutely be keeping him hostage or keeping him from going. But unless he specifically asks you for help you can do nothing else.

And since the above would be considered abusive since he is literally disabled they will get involved. Trust me on that.

Good luck!