Many have varying interactions with the darker sides of life, but usually don't admit it.
Edgar Allen Poe's "The Oval Portrait" has some parallels with Oscar Wilde's "The Picture of Dorian Gray" but written some 50 years earlier. We are subliminally interested in the blend of love, life and our mortality. Indeed it has always been a big subject with Woody Allen also and countless other writers.
It is a sensitive subject, but many truly do struggle with inner demons as too much gets on top of us. Look at all the suicides in Ireland and indeed the recent sad case of the mother who appears to have killed her children before taking her own life. Edgar Allen Poe himself was a very troubled individual but it may have helped him a little to write his macabre tales.
One of my daughters is a student psychiatric nurse. She is very professional about never mentioning names but in general terms seems to come across such a range of problems which very ordinary people have. Psychiatric problems seem to be on the increase.
My attitude in life is to see the funny side as much as possible, certainly it helps me. My wife is the same and in addition she has often said that those who are contemplating suicide should force themselves to go out and do something useful for others. If the inner pain is too much to live then maybe project outwards and just help someone else in a small way, even as a last deed. I would think it could be very therapeutic for the troubled person.
I don't pretend to know near enough on the inner demons and darkness which people go through. It's too big a subject for me but such a growingly important topic in today's world.