This is really masterfully done. Truly. I've accepted your premise with no problems, but the way you have fulfilled the premise is what is simply dazzling me. Both D and E vastly underestimated the complications of the bargain they made with each other, and to understand their thoughts as they come to realize this is fascinating. And you're such a deft hand at Wickham - you haven't overblown him at all. The way he is subtly attempting to lay a foundation for a future relationship with her (does he envision himself as her lover, being fed a steady diet of cash gifts and then blackmailing her when things go sour?), as well as the little ways he mistakenly overplays his hand, these are quiet touches of brilliance. I hope Elizabeth is truly growing some esteem for Darcy, if she never did I could see contempt for him in her future. I feel a great deal of pity for Darcy's emotional position here, even though he is quietly arrogant he is so vulnerable to her. Oh, I hope she treats him kindly. E could really hurt someone with her tendency to be flippant about serious subjects. The mild annoyance of D's habitual superiority pales in comparison to the damage E could do to his heart.
Readers can debate all they like about the characters, their motives and their decisions, but nothing you're writing here feels forced or out of key.
