The Blue Angel

Immanuel Rath (Emil Jannings) is an esteemed educator at the local Gymnasium (a college preparatory high school) in Weimar Germany. The character is crafted to embody the essence of the provincial Weimar German lower middle classes; the "Petite bourgeois", whose politico-economic, and moral ideology is wholly a performance imitated from their interpretation of; and their subservience to; the mores of the haute bourgeoisie, which they the petite bourgeoisie seek to identify themselves with; and who, in bourgeois morality, they strive to imitate.
Motivated by this this, Rath (in his role that he believes is that of guardian of the purported standards of the haute bourgeoisie; through the moral education of youth, at the Gymnasium) punishes several of his students for circulating photographs of the beautiful Lola Lola (Marlene Dietrich), the headliner for the local cabaret, "The Blue Angel". Hoping to catch the boys at the club, Rath goes there later that evening, to meet and confront Lola herself. His experience at the cabaret is however, not what he had expected. And his sense of "mission"; as the guardian of moral rectitude and the mores of the haute bourgeoisie; simply vanish, as the fictions that they always were.
Rath's all consuming desire for Lola, becomes his new personal mission. When he returns to the night club the following evening to return a pair of panties that were smuggled into his coat by one of his students, he ends up staying the night with her. The next morning, reeling (yet liberated from his self-inflicted false imprisonment) from his night of passion, Rath arrives late to school to find his classroom in chaos and the principal furious with his dÃ©classÃ© behavior.
Rath's position at the academy becomes untenable. He can't (at one and the same time), pretend to his students and fellow faculty; to stand for the derision of low morals. Yet, to personally indulge himself, in the servile obsequiousness of the much older man; who is spending all his free time with a woman who is young enough to be his granddaughter. So he eventually resigns from his position at the academy to marry Lola (to be with her sexually; and to observe certain legal and moral practicalities, all in pursuit of a now no longer y repressed lust for women).
But of course their happiness is short-lived, as Rath becomes humiliatingly dependent on Lola. After several years he is forced to take a position as a clown in Lola's cabaret troupe to pay the bills. His growing insecurities about Lola's profession as a "shared woman" eventually consume him with lust and jealousy. The troupe returns to his hometown and The Blue Angel, where he is ridiculed and berated by the patrons, the very people he himself used to deride. As Rath performs his last act, he witnesses his wife embrace and kiss the strongman Mazeppa, her new love interest, and is enraged to the point of insanity. He attempts to strangle Lola but is beaten down by the other members of the troupe and locked in a straitjacket.






Marlene Dietrich in The Blue Angel
Later that night, Rath is freed and makes his way towards his old classroom. Rejected, humiliated, and destitute, he dies in remorse, clenching the desk at which he once taught.

Question: What drives Rath insane?
Answer: Watching his wife kiss the strongman