As Kathy said, Darcy did conspire with his sisters over Bingley's fate, and though Darcy certainly does not want to marry Caroline, many of their conversations together suggest that their relationship was more than just superficial. He would never allow someone whom he just tolerated to tease him like Caroline was doing.

I'm sure she would have been trying hard to gain Darcy's attentions even before Hertfordshire, but I feel that Caroline's wheedling and cattiness became prominent only after the 'fine eyes' aftermath. Because of her jealousy towards Lizzy, all her baser instincts came up to the surface.

As the Bingleys and Darcys seem to be in company most of the time, Darcy does not seem to have had any scruples as to her influencing his sister.