Does Devin's father even exist?

This might be a dumb question, but I’m just curious — does Devin’s father/Sara’s husband actually exist? I thought he was just a fictional character.

Because if the father really was waiting for them in Crook Springs, they wouldn’t have decided to head to California after coming so close.

Also, why were they so desperate to get to Crook Springs? What makes that place safer than anywhere else?

Btw who was the man Sara killed in Boston for abusing her and Devin? Was it her husband or someone else?