On page 163 of The Giver, why did things "fall apart"?
It is always problematic using page numbers as depending on the edition of the book they may be different. In future, please reference particular events by refering to specific chapters. From your question, I am guessing that you are talking about the events of Chapter Twenty-One, in which Jonas is forced to swiftly leave the community which has been his home all of his life due to the announcement made by his father that Gabe is going to be released the very next day due to his lack of progress and development. Let us remember that Jonas has just discovered the true nature of being "released" thanks to the video that the Giver showed him of his father releasing the twins before. In spite of his plans to slowly work on changing the community from within, this forces the hand of Jonas and he is forced to run away from the community with Gabriel in order to save his life.