in love with the family laundry maid and kept her as his mistress for many years (during Tudor period), Darcy cannot make a mistress or, in his opinion, a wife, of Elizabeth.

Granted that Elizabeth is not a laundry maid, but she is not of Darcy's class, she has no money, and she has a family that is irritating in the extreme. If they were to marry it is my understanding that her social status would rise to his, as she would be marrying up, but it still leaves the question of money and that family. So, yes, there is danger for Darcy given his attraction to Elizabeth (don't see any evidence that it is love) under seemingly hopeless circumstances.