My theory, not take it too serious!?
Wufeng spy 20 years ago is ML mother, she also said all truth to her son, and whole bride selection and everything it's trap for Wufeng, like give them fake information and deceive them.. also ML from beginning knew that YWS is spy, but he fell for her from the start, because she reminds him his mother who also was trapped and used by Wufeng and had miserable life , but had kind sincere heart.
That prostitute girl also is spy (can see from BTS she not that simple) , and works for ML.
So at the end FL with ML and some other people will works together against Wufeng