Edgar still hasn't told his father who he really is. But he has decided to fight in the battle on the side of Lear and Cordelia.
He stashes Gloucester beside a tree and tells him to hang out until the battle is over. Then he runs offstage.
Edgar runs back onstage and informs his father that Lear and Cordelia have lost the battle. (What? You were expecting something else from Shakespeare's greatest tragedy? Now would be a good time to prepare yourself, because it gets a whole lot worse.)
Predictably enough, Gloucester starts talking about suicide once more. Edgar tells him to cheer up and leads him offstage.