What does Cosimo tell Viola about a decision and what happens when he tells her?

Cosimo tells her of his resolve never to come out of the trees--he confesses to her that he has not been on the ground since the day he told her he never would. He so instantly and completely regrets his confession that when he loses his footing during a fit of rage at the boys' laughter and falls, he does nothing to stop himself from landing hard wherever he may. Fortune snags his coat on a branch, and Cosimo remains hug there, firm in his resolve never to speak of his private law ever again.