Why was he feeling guilty? A parent's first responsibility is his own children. Does anyone seriously think that if humans caught an actual mythological dragon, then they'd ever let him go back to his family? The heck, I bet that they'll imprison (best case scenario) his family too if they get the chance. Body parts of mythological dragons are considered precious all over the world & a powerful creature, like mythological dragons, will always be killed eventually to ensure the safety of human civilians, no matter how intelligent that creature is. Practically speaking, a higher creature has no reason to sacrifice itself for a lower creature. His human "friend" was apparently a politician in an era when you can't trust politicians at all. Zero. Null. Nada. There's no way in hell that he didn't know that his secretly dragon "friend" will suffer a lot if he was discovered by humans. The human guy clearly chose family over friendship. The dragon guy did the same but still suffered from intense guilt.