Julie as the caged bird *spoiler*
He shouldnt have chopped of the head of that bird to drive her loopy.
Julie just wanted to escape from her spoilt and unfulfilled life. Thats why she proposed the menage-a-trois escapade to switzerland
He didn't chop the parakeet to hurt Julie. And Julie was not only trying to escape the Estate but, life itself.
Jean knew the Parakeet would die if released into "the world". It simply couldn't deal with the rough and alien world it would be entering if set free.
Miss Julie would not be able to handle the World either. This is Jean's moment of reality. Just as he realized that killing the parakeet is the merciful thing (compared to the bird starving in the wild and just being an easy kill for bigger birds). He realizes that allowing Miss Julie to commit suicide is the end of his fantasy but, it is possibly the kindest thing for her.
She has reached a low point of control where the next step for her is disgrace and possible institutionalization (which at that time would have been Hell).
He kills the bird, allows Julie to embrace her Fate (Death) and returns himself to superficial reality of service as a footman, all in one scene. He knows his scheme was mad. He knows it would have killed Miss Julie eventually. Just after more pain and disgrace.
His lovemaking with her....it was the final reality check. It would not magically overcome all the problems and barriers to his fantasies as well as hers.
And, not to be forgotten, Mis Julies death prevents certain disgrace to her father, his liege lord and idol. All at his hand. His actions simply minimized the damage to the greatest number of people. At the cost of his own hopes and dreams.
Brilliant acting performances from Miss Julie and Jean.