Kind of like how if you look at someone and assume they're struggling you'll be right, you can look at a problem or realistic story and assume it has been or will be a reality at one point.
If the darkess and depression in this story exist just because, it may do more harm than good to the readers. I mean this in the best way. With extreme sadness, you can bring characters through storms (and therefore readers) but unless there's a note of hope, or even a semi-happy ending, it won't quite be an honest story at all. Emotionally wrecking myself at the hands of a story should leave healing potential, or I'll be left wondering if it was worth it.
I think this has enormous potential and wish you luck on whatever you decide to write. (Whether this story or a different one.)