martin, for all his faults, at least knows when he’s being self-destructive. he is acutely aware, even. jon, on the other hand, will look directly at daisy and say “it’s all very rational, my back up plan for if I couldn’t get you out of the coffin was that it would just kill me and if that didn’t happen I was hoping that you’d just kill me.”
jon knows that depression and ptsd exist but he thinks he’s immune to them and that all his fantasies about being put down like a dog are merely the reasoned thoughts of a scholarly mind
or, to be fantastically blunt: jon doesn’t think he’s suicidal, he thinks he’s right