Dukat always had a very precise image of who he was; that being the stern but compassionate prefect of Bajor. Mistreated by his superiors, misunderstood by the Bajorans; but always living up to the ideals of Cardassia even when being a kind ruler to lesser races. Even the agreement to have his people join the Dominion fit that concept as the forward thinking of a patriot whom wanted his people to become strong again. The displays of disgust by the likes of Sisko? Just narrow minded Federation thinking the Captain stubbornly held on to rather than admit their shared status as great leaders.
The events of Sacrifice of Angels broke everything. Ziyal's betrayal of him and subsequent murder by Damar cracked the black and white view on what enemies of the state were. The Dominion retreat of the station ends his ideal opportunity to eventually best the Founders behind their back in the future. Intervention by the Prophets demonstrably proves Sisko was the savior of the Bajorans without equal. And the death his daughter destroys the most personal view of himself as the good father protecting his family.
In one fell swoop fate seemingly goes out of its way to shatter Dukat's plans and self image; delivering an existential gut punch that takes until the ending of Waltz to recover from. Faced with accepting responsibility for what his actions brought about, he instead just crafts a new delusion, that of a good man transformed into a Messianic destroyer because a cruel universe left him no other choice.