Shakespeare's scathing attack upon the morality of his mistress exemplifies their tumultuous and perplexing relationship. The three quatrains outline the poet's inner struggle to cope with both his lover's infidelity and the embarrassing self-admission that he still desires her to gratify him sexually, even though she has been with other men. The poet yearns to understand why, in spite of the judgment of reason (5), he still is enslaved by her charms. Confused by his own inexplicable urges, the poet's whole being is at odds with his insatiable "sickly appetite" (4) for the dark lady. He deduces in the final quatrain that he surely must be insane, for he calls his mistress just and moral when she obviously is neither. Not until later sonnets (150-1) do we see a change of tone and a cool-headed acknowledgment of the recklessness of the whole affair.
In Sonnet 151, the poet admits that he cannot continue the relationship because it betrays his "nobler part" (6) i.e. his soul, and in Sonnet 152 we are witness to the end of the affair.
Is Sonnet 147 autobiographical? Did Shakespeare really have an affair with a raven-haired seducer? Critics are divided on this matter, and, until some new documents are uncovered, we shall never know the truth. Attempts have been made to solicit possible historical candidates for the role of the dark lady, based on their likely association with Shakespeare. The most famous contenders are Mary Fitton, lady-in-waiting to Queen Elizabeth; Lucy Morgan, a brothel owner; and Emilia Lanier, the mistress of Lord Hunsdon, patron of the arts. I'll leave you with a skeptic's view of the autobiographical nature of the sonnets:
Every sonneteer of the 16th century, at some point in his career, devoted his energies to vituperation of a cruel siren....In Shakespeare's early life the convention was wittily parodied by Gabriel Harvey in "An Amorous Odious sonnet entitled The Student's Loove or Hatrid, or both or neither, or what shall please the looving or hating reader, either in sport or in earnest, to make of such contrary passions as are here discoursed". The Dark Lady of Shakespeare's sonnets may therefore be relegated to the ranks of the creatures of his fancy. It is quite possible that he may have met in real life a dark-complexioned siren, and it is possible that he may have fared ill at her disdainful hands. But it was the exacting conventions of the sonneteering contagion, and not his personal experiences or emotions, that impelled Shakespeare to give the dark lady of his sonnets a poetic being" (Tyler 359).