A dark cully is defined in Grose's Dictionary of the Vulgar Tongue thuslyly:
DARK CULLY. A married man who keeps a mistress, whom he visits only at night, for fear of discovery.
I rather like the idea of this worried husband running around in the dark, bumping into things and fearing for his wife. It also reminds me of the fantastic passage in the biblical Book of Proverbs, even though here it is the other way around:
For at the window of my house I looked through my casement, And beheld among the simple ones, I discerned among the youths, a young man void of understanding,Passing through the street near her corner; and he went the way to her house, In the twilight, in the evening, in the black and dark night: And, behold, there met him a woman with the attire of an harlot, and subtil of heart. (She is loud and stubborn; her feet abide not in her house: Now is she without, now in the streets, and lieth in wait at every corner.) So she caught him, and kissed him, and with an impudent face said unto him, I have peace offerings with me; this day have I payed my vows. Therefore came I forth to meet thee, diligently to seek thy face, and I have found thee. I have decked my bed with coverings of tapestry, with carved works, with fine linen of Egypt. I have perfumed my bed with myrrh, aloes, and cinnamon. Come, let us take our fill of love until the morning: let us solace ourselves with loves. For the goodman is not at home, he is gone a long journey: He hath taken a bag of money with him, and will come home at the day appointed. With her much fair speech she caused him to yield, with the flattering of her lips she forced him. He goeth after her straightway, as an ox goeth to the slaughter, or as a fool to the correction of the stocks.
Whatever happened to girls like that?
The Inky Fool catches forty winks.