OC posting again but I love thinking about why, exactly, the original Vault Dweller left their family in Arroyo.
All of Adam's companions died in fo1 and he just had to kinda... keep going. He was sixteen years old and all his friends who are older and smarter and tougher than him were dying and he had to keep going because if he dies then everyone he loves in the Vault will die too.
And then he saved everyone! And furthered the progress of civilization! And then wasn't allowed to go home ever again.
And while Arroyo does become his home, mostly due to Pat and the kids, he isn't ever gonna be okay. Even in a village the wasteland is dangerous and his hypervigilance is justified in a lot of circumstances. But as his kids get older and when his son turns sixteen he realizes that he was a BABY. His son is just a dumb kid and oh my god he was so much dumber and he should not have been the one saving the world.
And he gets a little better! And he's older and smarter and he's been leading these people for so many years that he's pretty secure that nothing catastrophic is gonna happen but the chance is never zero.
But as he gets older and older and his kids are getting married and taking up big responsibilities in the village the dread starts to creep back in and he loves Pat. He loves her so much and he couldn't dream of life without her, but then his hair starts to thin and his hands are bony and he bleeds a little too easy and one day he gets a scratch and it peels his flesh away like it's not even attached to him.
He's turning into a ghoul. And he remembers Necropolis and he doesn't want that to happen to his home, but when he looks around he's the only one who's getting sick. He's the only one falling apart.
And so he leaves. His people are already adapted to tribal ways and really his family does most of the governing now. So he leaves his suit and his Pip-boy and decides that he'll watch them from a distance. And he leaves a letter for Pat that apologizes for leaving and for the ways his past made him mean and distant and asks her not to look for him because he doesn't want to be found.
He does it because he's tired of hurting his family and because he doesn't want to stick around just to see them die and because he doesn't want to see them stop needing him at all. He leaves and thinks that if he just keeps his distance then it won't hurt as bad and that he can wither into immortality in silence and that he can die in obscurity and that his family won't have to deal with being tied to The Vault Dweller forever.
And then Pat dies, and his son dies, and he wishes that he could die but he won't do it himself. And then he learns about his granddaughter. Lamia, the Chosen One. And he realizes that the only thing he did by leaving was running away, and that he's too much of a coward to go back and admit that he should've never left at all.