Can it be that after Ramsgate, Georgiana has lost some of her spirit. It must have been a terrible disappointment for her to realize the man she had known as a child and was prepared to trust for life, was only after her money.
Darcy would be very desirous to repair the damage by finding her a goodnatured and kind husband without mercenary motives. Not too surprising if the possibility of Bingley, his other protégé, whom he knew and trusted(and could easily manage ;-9) had occurred to him.
I think he was feeling protective for both their sakes and excessively careful, suspecting any prospective marriage partner of greediness.
The idea of marrying for love was still a luxury, was it not?