If you've known him 25 years, how come the only way to contact him is on Messenger? Did he block you on his cell phone?

So, the bottom line is: you must stop pushing this with him. You must stop contacting him. He doesn't want your help, he doesn't want your friendship and he doesn't want a relationship. I agree with divine. This is borderline harassment. You've got to respect his desires and leave him alone.