Why would you want to or consider telling her?
If you genuinely did not know he was married and you've discovered he'd deceived you both, there would be good reason to. But you knew. You KNEW.
Hell hath no fury like a woman scorned, as they say.
I think if you did choose to tell her it would be purely for revenge.
Revenge on her for finally winning the prize (🤷♀️) you wanted, so the loser lashing out would hurt her, like a drone strike dropping a bomb into her life from a safe distance.
Revenge on him for not following through with the mirage, the outcome he dangled in front of you in return for a fuck.
The 'huge betrayal' ? That was committed by you. Against all decency, kindness, morality, and deliberately harming a complete stranger.
Don't try to kid yourself or us that it would be the kind thing to do. There's no kindness here.
And beware - if you chose to do something that could take away his cushy life, you'd have no way of knowing how he'd react and it could be dangerous for you. They can turn very nasty indeed.