Why does Derek feel no one will kiss him ? Why does he hate being kissed by her mother ?

Derek believed that no one would kiss him because his face had been disfigured by acid and most people found his appearance  revolting. He believed that only his mother would kiss him and that too on the other side of the face. He did not like it when his mother kissed him because he felt that she did so because she had to as his mother and not out of affection.