Why does Darcy verbally distance himself from Elizabeth? How is she any harm to him?
Darcy is a very wealthy young man who believes that people of character and breeding should behave a certain way. When he encounters Mrs. Bennet and her younger daughters at a party, he finds their garish behavior revolting, insulting and makes a point to stay away from the Bennet sisters.
He believes that it is in his best interest to keep his distance from Elizabeth. Once he realizes that he has fallen in love with her, he is desperate to stay away from her for fear that he will suffer greatly loving her from a distance.
Darcy is determined to keep his love for Elizabeth in check, to get over it like an illness. Unfortunately, his plan to stay away from her fails. He encounters her when she visits Mrs. Collins, who lives near Lady Catherine de Bourgh.
Darcy is so stricken by his love for Elizabeth that he walks over to the house she is staying in and asks her to marry him in a most clumsy and insulting manner, saying that he has decided that he needs to marry her because he can't forget her, he cannot get her out of his mind. Elizabeth rejects his proposal, exclaiming that he is a rude, ungentlemanly individual that she would never consider suitable as a husband.
He vows then, to keep his distance from her out of respect for her decision.