I've inserted Shakespeares' Sonnet 147 into the monologue so I've been thinking about it quite a bit lately.
In most of his work, and in fact most of Sonnet 147 itself, Shakespeare is all about extended metaphors and clever wordplay. Sonnet 147 is mainly a metaphor comparing reason to a physician and love to a disease:
My love is as a fever longing still,And then he drops all the intellectual niceties and practically screams the last lines:
For that which longer nurseth the disease;
Feeding on that which doth preserve the ill,
The uncertain sickly appetite to please.
My reason, the physician to my love,
Angry that his prescriptions are not kept,
Hath left me, and I desperate now approve
Desire is death, which physic did except.
Past cure I am, now Reason is past care,
And frantic-mad with evermore unrest;
My thoughts and my discourse as madmen's are,
At random from the truth vainly expressed;
For I have sworn thee fair, and thought thee bright,Like so much of Shakespeare's sonnets, even people who are very familiar with Shakespeare and his late-16th century mode sometimes struggle with teasing out the meaning. But anybody can understand those last two lines, no translation necessary. The last line could be from a heavy metal song.
Who art as black as hell, as dark as night.
You can see how variously the sonnet has been interpreted on Youtube.