In Pride and Prejudice, what is Mr. Wickham's motivation especially toward Lizzy, and how does it change through the story, if at all?

Mr. Wickham's primary motivation in the novel is to marry
for financial security.  He is arguably the most selfish character in the novel.  When
he is first introduced he is presented as a charming man who has definite romantic
interest in Elizabeth, but once it becomes clear that she will not have much of an
inheritance, he quickly shifts his attentions to Miss King who has a comfortable amount
of inheritance in the bank.  Lizzy isn't all that interested in Wickham and actually
defends this action to her aunt when they talk about what Wickham has done.  Lizzy fully
understands the necessity of financial security, even if she isn't willing to marry for
it.  At this point in the novel she still believes Wickham's story that Darcy hasn't
been fair in regards to his inheritance from the Darcy
estate. 

As the novel progresses we learn that the
relationship with Miss King has fallen apart and that Lydia is very interested in
Wickham.  Unfortunately, Lydia is very naive and foolish -- she runs off with Wickham
and creates a complete scandal.  Wickham has no intention of marrying a Bennet daughter
-- they have no money!  Wickham only agrees to marry Lydia when Darcy bribes him with an
incredible amount of cash and a commission in the military (higher rank).  By this time,
Elizabeth knows that whole story of Wickham's lies about Darcy, and she is appalled that
her sister now has to be married to the man, but she is relieved that a family scandal
has been avoided.  When she later learns that the marriage came about because of Darcy,
her feelings for Darcy are cemented.  She ultimately marries him for love and tolerates
Wickham as a brother-in-law.