“Make my breast
Transparent as pure crystal, that the world,
Jealous of me, may see the foulest thought
My heart holds.”

— George Villiers, 2nd Duke of Buckingham

Beaumont and Fletcher Philaster, Act III, sc. ii, line 144.
These lines are used almost unaltered ("holds" becoming "does hold") in Act III, sc. ii of Buckingham's The Restauration, an adaptation of Philaster. They appear with an attribution to Buckingham in many 19th century collections of quotations, e.g. Henry George Bohn A Dictionary of Quotations from the English Poets (1867) p. 63, and hence also on several quotation websites.
Misattributed

Adopted from Wikiquote. Last update June 3, 2021. History

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George Villiers, 2nd Duke of Buckingham 20

English statesman and poet 1628–1687

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