Quote 1
"Hey, son," his dad said, his voice bending in that weird way that America had started to shape it. (12.37)
Not only does Conor's dad move away from him physically, he moves away from him verbally, too. Everything in Conor's life is changing, even his dad's accent.
Quote 2
"Your mum's taken a turn, Con," his father said. Conor looked up quickly. "Your grandma's gone to the hospital now to talk to the doctors." (18.18)
Notice that his dad doesn't even have to say "for the worse." Even as he continues to cling to the hope that his mother will get better, Conor knows she's getting worse. At this point, he doesn't need to hear the truth spoken. He's starting to admit it to himself.
Quote 3
"Son," his father said, leaning forward. "Stories don't always have happy endings." (20.42)
This is the best Conor's dad can do at telling him the truth. It's just as vague and complicated a story as the ones the monster tells, and a lot less helpful. Which raises a question: does Conor's dad's presence relieve some of his suffering? Or does he just make things worse?