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I have sworn thee fair, and thought thee bright, Who art as black as hell, as dark as night.
— William Shakespeare · Sonnets

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker sets earlier praise against a fiercely opposed present judgment. “Fair” and “bright” give way to hell and night, making disillusionment visible through a reversal of light and dark. The bitterness is intensified by admitting that the former admiration was the speaker’s own.
Context reviewed