Evan was so distracted by the truck, that he was completely oblivious to why the truck was there, and couldn't comprehend that his father was leaving for good.
Mrs. Hansen feels lonely and has grief because they are all alone their house, which feels bigger due to the empty space from the absence of Evan's Father. Mrs. Hansen feels like she let him down and it's all her fault.
Evan finally realized that his dad is gone forever and doesn't know if there is "another truck coming to our driveway? A truck that will take mommy away," because he was worried that his mom would abandon him too (Jones 16-17).
Mrs. Hansen thinks it’s all her fault that Evan doesn’t have a Dad. She is never around to be there for him, so Mrs. Hansen feels even more guilty about Evan is so scared that he will be left with no one to love him.
Mrs. Hansen is committed to supporting her son and helping him realize that "no matter what, I'll be here,", showing that she will do anything for Evan to be happy again (Jones 33-34). This supports the theme that someone is always there for you no matter how alone you feel.
Mrs. Hansen is trying to have Evan understand that no matter how big or small things may feel, she will be there for him. The tone is depressing but the mood is sympathetic.