If so, what was he so unhappy about?
His life was in shambles. He was aging, had no money, couldn't find decent work, and lost his sugar mama.
I remember seeing something many years ago that suggested he had his button pushed.
I don't know about "aging"- he was only 45.
...
Suicide is one theory ... murder is another. The cast of Superman (i.e., Jack Larson, Noel Neill) always thought that George was murdered by a jealous boyfriend.
I don't believe so. But we'll never know.