That’s the neat part, you don’t. At least, I don’t think you’re ever truly cured of depression or any other mental illness. You just learn to manage them, take steps and avoid the things that make them worse, and you do that for the rest of your life. It does get easier, but it never goes away. And you end up in a situation that exasperates your mental illness, or you stop doing the steps and let things get out of control and you’re right back where you were before, maybe even worse.