@Hurt Bunny,
That's a very interesting question. Should a married woman be best friends with a single man or even another married man? Should a gay partner be best friends with another person of the same sex as the gay person?
Do married couples have to be best friends too?
Quite obviously, most people can't handle such arrangements, and for the current situation, would the married man be comfortable with you, the wife, being best friends with another male, married or single?