Comedies of manners are works that find their height of popularity in the early and mid 1800's. Jane Austen, Oscar Wilde, George Bernard Shaw, and other greats, represent this genre. As a technique, their works depict the idiosyncrasies of the different social classes while over-emphasizing, and somewhat exaggerating, the traits that make those very classes feel too big for themselves.
However, love and friendship are also themes that show up in those works, considering that Pre-Victorian and Victorian England were times when the social growth that was brought in by the advent of Industrialism also propelled changes in the ruling classes, initiating the creation of etiquette- and increasing the need for social relations.
This being said, social interaction was a daily bread; one which consolidated marriages, networked with the "fashionable society", and gave way to the social growth-or death- of individuals.
Therefore, in comedies of manners such as those of Austen, and plays such as The Importance of Being Earnest, friendship and love follow the same line of mentality of their time.
For example: Friendship in Pride and Prejudiceonly occurred among people of the same social class. Jane Bennet's friendship with Miss Bingley proved to be a fiasco of a hypocritical nature, in which the poorer woman was left hurt and humiliated. Those with similar tastes and habits would make good friendships. Anything beyond what they know is considered "undesirable".
Similarly, in The Importance of Being Earnest, Algernon and Jack base their friendship in those same common interests that are unique to the upper class dandies: Eating excessively, causing a trail of havoc, behaving naughtily and escaping responsibilities were the characteristics that made them so similar. Again, friendship is mostly a symptom of social connection.
Love is also a debatable topic: Austen sees love as an unattainable dream, since marriage is meant to be another social networking transaction. Only the true Austen heroines will find true love. Following the same line of thinking, other comedies of manner such as Wilde's, see the institution of marriage as a tedious obligation in which true love cannot be found except....outside of the marriage!
Therefore, the need for society and the desire for climbing the social ladder made friendship and love two opportunities for networking, rather than the philosophical ideals of altruistic capacity and emotional sharing. Those were not the ideals of Pre-Victorian and Victorian England- at least not in this particular genre.