Virtue describes morally “right” behavior, as defined by a given society. In our case, the most virtuous action would be for the boyfriend to tell his girlfriend that he has genital herpes, the primary goal of this action to prevent the girlfriend from experiencing unwanted physical harm (i.e. to allow the girlfriend to choose whether or not she wants to expose herself to genital herpes. Given this main goal, the next most virtuous action would be for the sister to warn the girlfriend of this herpes risk. This means that the most virtuous action changes depending on the context of the situation (i.e. the available actions). (Merriam-Webster's online dictionary, 2016)
Non-malfeasance is defined as a non-harmful behavior; this includes physical and mental/emotional harm. It can be assumed that physical harm should be avoided at the cost of mental/emotional harm if the physical harm causes permanent damage or prolonged distress; this can be gauged by what decision we would want someone to make on our behalves in the same situation. In this case, the girlfriend is at risk of contracting a permanent and uncomfortable virus that may not be avoided by condom-use during sex. This means that physical harm should be avoided before the lesser and greater amount of emotional damage that would occur (to all three people involved) if the boyfriend revealed that he had herpes, and if the sister revealed her brother had herpes, respectively. (Merriam-Webster's online dictionary, 2016)
We describe honesty as fairness and informational transparency. In our case, only one of the involved parties (i.e. either the sister or her brother) needs to inform the girlfriend of her boyfriend’s transmissible virus for the purpose of honesty in this case to be achieved (i.e. for the girlfriend to know that she may expose herself to genital herpes if she has sex with her boyfriend), so not everyone in this case needs to be honest, as long as one person is before the girlfriend is exposed to the virus. Given the above descriptions of virtue, non-malfeasance, and honesty, the boyfriend should tell his girlfriend that he has genital herpes before they have sex; and, if the boyfriend tells his sister that he is not going to do this then the boyfriend’s sister should tell the girlfriend that her boyfriend has herpes. This order of potential events ensures that no unwanted harm befalls the girlfriend, and that the least amount of emotional harm is incurred while honesty is maintained, with the primary goal of keeping the girlfriend from physical harm and limiting emotional harm for all three people involved in this case. (Merriam-Webster's online dictionary, 2016)
This answer also demonstrates that virtues and moral values do not conflict with each other if we prioritize our actions and are aware of our ultimate goal; this means that we do not need to complete all of the virtuous actions available in an event (in this case that would be telling the girlfriend that her boyfriend has herpes). Sometimes, somebody else most virtuously achieves the primary goal of an event. Our virtuous action could instead be one of informational omission with the effect of limiting harm. For example, in our case, by not telling the girlfriend that the boyfriend has herpes before the boyfriend reveals this information, the sister prevents hurting the boyfriend and the girlfriend. This also demonstrates how excellence and the golden mean can be applied to this case; the sister does not need to be honest in all of her interactions with the girlfriend about the boyfriend’s herpes if the sister’s actions result in the most virtuous outcome (i.e. protecting the girlfriend from physical harm and protecting everyone involved from as much emotional harm as possible).
After the “New Development” occurs, the sister should tell the girlfriend that the boyfriend has genital herpes. This is assuming that the sister cannot convince the boyfriend to reveal this information himself, and this is also assuming that the sister would reveal this information in the way that does the least amount of harm to her brother and to the girlfriend (i.e. adhering to the principles of virtue, non-malfeasance, and honesty). This includes the sister being honest with her brother about what she is going to tell the girlfriend, and expressing to the girlfriend that her boyfriend cares very much for her, and just held misconceptions about genital herpes’ transmission.
Honesty. 2016. In Merriam-Webster.com.
Retrieved May 8, 2016, from http://www.merriam-webster.com/dictionary/honesty
Non-malfeasance. 2016. In Merriam-Webster.com.
Retrieved Jan 15, 2016, from http://www.merriam-webster.com/dictionary/non-
Virtue. 2016. In Merriam-Webster.com.
Retrieved Jan 15, 2016, from http://www.merriam-webster.com/dictionary/virtue