I am going to assume that both questions deal with the first half of the book, and not the events of the second half.  In regards to the ball at Netherfield, Wickham decides that "scenes might arise painful to more than himself" if he were to meet Darcy at the ball.  Therefore, he avoids it.  This is based on his past with Mr. Darcy - Wickham claims that he himself was supposed to have received the job as minister of the Darcy family's church, a job promised in old Darcy will.  However, Wickham insists, the son refused to honor the father's wishes and Wickham was left out in the cold.  We learn later what the truth of that is.

After flirting with Elizabeth Bennet for a few weeks, Wickham is seen with Ms. Mary King.  He clearly tries to pursue and marry her because she has just inherited a fortune.  This plan will eventually fail, and he will not be Ms. King's husband.  Later in the novel, he is forced into a marriage with Lydia Bennet.