how did everyone manage to keep the truth from celphi for this long?!!

About the kidnapping? Maybe cuz it was only for one day so they were able to made up a lie and that child is smart he knew they were hiding something so maybe he knew something has happened that's why he pretended to be sick to stay at home.

and I love the fact that the Duke doesnt leave him out of the situation for long.
its awful to be treated as a child who knows nothing and being left behind.