Do you remember now those love letters to the world you sent from Australia? Now you’ve asked, “Who am I without depression?” You are not a full person without depression. Because you are incomplete without it. It has been a part of you for so long. But that doesn’t mean it is who you are. That doesn’t mean depression defines you. You wear it, like that Ancient Mariner wears his albatross.
All writers, all gifted people, wear this, and you were “fortunate” enough to live in an environment where the people you loved enhanced that weight upon your shoulders to an extreme. Perhaps someday that “good fortune” will work some great magic for you as it has for some others.
Nothing is going to change this and you are absolutely correct, you will not locate some single, traumatic moment, some “AHA” that you will be able to turn into a sunny day so that your life will become a rainbow filled with dancing unicorns.
But the unicorns and rainbows are there, none the less. You reveal them all the time. In your writing. They, in your writing, are the best companions, along with your depression, to shield you against depression's worst effects.
The saddest thing—and I know this personally—is that you may not have a therapist especially gifted in dealing with artists, someone who can clearly understand this particular layer of the psyche.
Should you give up the therapy? I know how tiring it can be when you are only banging your head upon a wall and repeating the same empty lines over and over. If you cannot try a new tactic and cannot go elsewhere to do so, yes, at least rest for a while. But tell her why, of course. And keep in your mind a goal to find someone who can help, and go back.