Most clinics have non-government sponsored sliding scale. Do me the favor of calling around and finding out. I know Catholic charities does sliding scale.

It's not your responsibility to prevent/protect loved ones from their demons. That's unfair to both of you and controlling. Now encouraging him to get help is fine, forcing it is not. This is not a thing you could love him out of. Honestly I don't think you should read the letter. It is not your fault that this happen.