Since I guess later in high school was when I started to be honest with the kind of darkness that was overcoming me. Not really, outright suicidal, but, more of a passive nihilism. I was only really suicidal post-covid; at that point I just felt it was quite obvious I was doomed to an empty and meaningless existence until I just dropped dead and nobody cares. But I guess said passive-nihilism, that would continue to grow to that point, had it's very start some time in middle school.
So I guess you could say I noticed post-covid, though I was still distracting myself as much as possible from this darkness until I've heard news of Canada's MAID program, then this forum from Tentacrul. Until then, I just focused on completely ignoring and negating this despair, but thanks to this forum, I saw that there where alternate ways to process this darkness, then the modern psychological/gaslighting/drugging approach that society pushes, as effectively the only way, that I continue to feel is incompatible with how I am and the simple reality of this world I'm in.
But again, if you want the "Root Cause", I'd have to say it's due to the way I was born, being autistic, and this completely fucked world that's getting hard on normies let alone someone like myself.