You have survived everything you have been through, and you will survive this too. Stay for the person you will become. You are more than a bad day, or week, or month, or year, or even a decade. You are a future of multifarious possibility. You are another self at a point in future time looking back in gratitude that this lost and former you held on. Stay.
As a person who lives with depression, the sentiment of this quote is solid. And the point it makes is realistic and fair. However, if I was in the depths of a depressive flair and I was told this by someone I trusted to share my despair with, this quote would just make me so angry. I don't know if it would help. I hope it helps someone else.