There are so many different takes on this situation. I will address only one. I am friends with a married couple and the man tells me that he thinks he may be gay. After he tells me that he begins to have an affair with another man. While I understand that his sexual need is different in both situations he has made a promise to his wife, also my friend, about their marriage. I speak to him and ask him if he has spoken to his wife both about his sexuality and the fact that his sexuality has driven him to have an affair outside their marriage. I tell him that I am equally friends with his wife and that I owe her a duty as a friend. I tell him that he must alert her that he is having an affair or end it. I would also tell him that whether he lets her know of his new found sexuality is his business. That may be something that they can work out in some sort of arrangement but that is not my concern. Giving him what I consider a reasonable amount of time to tell her, I would ask him again if he has told her about the affair or ended it. They actually may work out a situation where she allows him to keep the affair going considering the circumstances (highly unlikely but I have to give that a chance). If he has not told her then I have to tell him that I would tell him about the affair as they are both my friends but that I would not tell her about his sexuality. If she asks me who he is having the affair with I will say I do not know.