Why does katniss finally confide all of her worries to Gale? What does she tell him, and how does he react to her news?

After Katniss' conversation with Gale in the lake house, his subsequent beating and recovery, and the increased authority presence and crackdown, Katniss is convinced that the Capitol must be dealt with.

Gale initially agrees to run away with Katniss, believing they have a chance for love if they can get out from under the gaze of Snow and his surveillance. Katniss is not convinced and, as she mentions when the issue arises, love is a luxury she cannot afford. Her goal is to keep her loved ones safe and if the promise of a romance with Gale is necessary to sway him, then so be it. However, news of the uprising in District 8 foils their plans. Gale’s rebellious streak overrides any affection he may have for Katniss; he is actually disappointed that she would suggest running when she knows the revolution is brewing, especially because she is already in a position to become a rebel leader.