Jonas leaves his community when he finds out that Gabriel is going to be released. When Jonas finds out what release really means, he is shocked. He has no idea, like everyone else in his community
Jonas's plans are ruined in chapter 21, when he discovers that Gabriel will be released the next morning because he is not reaching his developmental milestones. In order to save Gabriel's life, Jonas needs to take Gabriel and flee the community on his own without any help from the Giver.