Even if their marriage does end, its a pressure she does NOT want or she would have told him herself. If she's hiding it for ANY reason - EXPOSE it...
WHo knows, she may be worried about finances and soaking him for money.. she may be squirrelling $ from him each week into a secret account and she doenst' have all his $$ yet who knows...
The point is, if she's keeping it a secret, its to your advantage then to expose it. THIS will put HER on the defensive for a change.. right now if it is secret then she is WIDE OPEN for you to sneak onto the offensive and expose over on her end.
Do it in her workplace if you have to... make a huge scene