My interpretation of the word is that it's used for 2 different people in the 2 instances you brought up.

In the first use of "danger" - it's Darcy that's in danger. He's in danger of feeling more than he ought for an impoverished gentleman's daughter with no good connections or fortune. He knows (in his head) that he should not be furthering this attraction by paying attention to her, but he can't seem to help himself.

The second "danger", imo, is directed at Lizzy. There is a real danger that he will pay her enough attention where she will be able to claim that he has lead her on and create a situation where he'll be duty-bound to offer for her hand. He avoids this (in his head only) very real danger by making sure he barely talks to her the last day she stays at Netherfield.