Not at all. Yuji Itadori's story doesn't end with his execution in the manga. There are many developments and challenges he faces, but execution isn't one of them.
Yuji Itadori survives till the end. The manga doesn't have his death as the final outcome. The story might have thrown challenges at him, but he manages to overcome them and remain alive.
It's hard to say exactly when friendship turns deadly in a true story. It could happen due to various circumstances and events that build up over time.
Itadori did indeed die in the manga. His death had a significant impact on the story and the other characters. It was a turning point that led to many new developments in the plot.