Response from David Brink on October 13, 2005

You don't have to be religious to think that trust and fidelity are important values that should regulate intimate associations. So, barring some special background that you have not supplied (e.g. the marriage is an "open marriage" or the wife has been in a persistent vegetative state for years), I would think that the extramarital affair was morally wrong, at least in part because it was inconsistent with marital trust and fidelity. It seems to me the unmarried woman does wrong if she knowingly enters such a relationship, even if it is not her vows that are being broken. If it's wrong for you to breach a contract, and I knowingly help you breach your contract, I've done something wrong. Moreover, if the unmarried woman genuinely cares for the married man, then she presumably has reason not to want him to do something wrong. So, to answer your original question, this gives her reason not to contribute to his infidelity. But this seems to be an additional reason not to have the affair, in addition to the primary reason not to facilitate infidelity.

Response from Matthew Silverstein on October 15, 2005

When I read your description of the situation, my first thought was that the woman has a responsibility not to protect the married man's vows, but rather to protect the married man's wife. After all, the wife is the one who is most likely to be harmed by her husband's affair, and it seems to me that we all have a responsibility not to act in ways that are likely to cause harm to others (even if we don't personally know the others in question). Of course, it is the man who bears the brunt of the responsibility in this case, since he has a specific obligation to care for his wife. Nonetheless, I do think that the woman is at least partly responsible for the negative consequences of her affair.