Ethan's father is not part of his life at all, due to leaving his mother after being abusive in the relationship. This quote contributes to his feeling of emptiness, like a piece missing literally and mentally. A father is a figure that children abide by and look up to, especially a son. His mother is affected as of he, contributing to his depression and anxiety. His dad has no input in his life so it leaves unanswered questions and thought provokes him into blaming himself.
Losing people throughout your life even if it's not to death still feels the same. A part of you dies depending on how much that person meant to you when you find out they weren't the person they portrayed themselves to be.