Friend of great heart and many sorrows, I am inadequate to cheering you. My experience of depression differs significantly from yours. You cannot escape the sadness; I cannot revive my dead will.
Who can blame you for how you feel? My doctors seem good only for keeping me alive. Really, is that good enough? I don't know, and I have little ability to care.
Oh, that I could give you back even a few memories! All I can do, though, is post my subjective affirmation: You have mattered. You do matter.
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My dog

mastered the "fetch" command. He would communicate he wanted something, and I would fetch it.