] One thing which has always puzzled me about JA's society is why it was considered so horrible for a man to break an engagement, even an unspoken one, while a woman could do it at will. [snip]

The only legal grounds that a man had for breaking an engagement were if the young lady was proved to be unfaithful or if he discovered that she had a compromised reputation (i.e. Lydia, if she hadn't married Wickham). The man breaking an engagement could be seen as an indictment of the lady's character and morals.

This is another reason why Darcy was so intent on keeping Georgiana's near elopement such a secret. Sure, Wickham would have looked bad but Miss Darcy could have expected this to come up time and time again with every prospective suitor. Lydia needed to marry Wickham because it was extremely unlikely that anyone else would ever marry her. A sister who had "lived in sin" with a man not her husband could not ever come back home lest she compromise the morals of the others. This is why Mr. Collins is surprised that the Bennets receive Lydia and Wickham and why Kitty is never allowed to visit Lydia after her move North.

A man who wanted out would have to ask the lady to release him from the engagement and she didn't have to do it.

Remember, these people didn't have television. They followed the lives of their neighbors with the same fascination and speculation that we do soap operas. Marriages, engagements, break-ups and reputations were topics of discussion which would have been chewed over for years by the neighborhood. People literally had to move elsewhere to get away from it.