What does the cryptic crossword clue "Perhaps sinner and saint going out — they often meet in the dark (8)" mean?

The definition is "they often meet in the dark". The wordplay uses a cryptic definition. Cryptic definition The answer is CURTAINS.

Perhaps sinner and saint going out — they often meet in the dark (8)

Times Cryptic #28966 | 18 Across | 2024-07-11 flower