I was going to say just this. If he's already worried about his licence then he would have to be a lot stupider than he sounds to write a 'true' goodbye letter.

Eta: wrote before read the rest but perhaps weight of views can help change your mind

I also think Anne may have something with the confirmation bias.

As for fixable- for me I pray it is and I think it is cause I am getting better but I hear your difficulties in this area.

Eta: maybe being stoic is how he holds in his emotion. You'll not catch me crying and showing vulnerability. You'd think from my outside appearance I was just see you later alligator but be dying inside. So maybe that's him? He felt he had to be the strong one?