What episode does Kurt leave the new direction and join the warblers?

Kurt Hummel leaves the New Directions and joins the Warblers in Season 2, Episode 15 of "Glee," titled "The Power of Madonna." After feeling isolated and bullied at McKinley High, he transfers to Dalton Academy, where the Warblers, a more accepting group, welcome him. This change marks a significant moment in Kurt's character development and his journey towards self-acceptance.