Although in almost any other industry, such a cartel, operating out in the open, would be a perseviolation of the antitrust laws, no one has directly challenged the NCAA front-and-center on whether this aspect of the cartel is illegal.
But, since that means adultery perse is not a violation, the air force could well have avoided much of the embarrassment of the Flinn case (it could, for example, have offered her a non-judicial punishment rather than a court martial).