Stan isn't your friend if he is holding your husband hostage about seeing him. A lot depends on how close you actually are to this Jan. If your husband was sneaking around with another woman, would you want her to tell you? He's been seen at least twice by you, he's surely not invisible to the rest of the world, and sooner or later, it's going to come out. I think she might be more hurt if she finds you knew and let her go on like a fool thinking he was working. On the other hand, this is a big thing and likely to break up their marriage, so make sure that you are very careful and gentle when you tell her. Just tell her only what you exavtly saw... maybe you can somehow mention that you saw her husband having breakfast with a woman friend, not mention what they were doing, just as a way to start her getting suspicious, so it won't come as a big shock. Casually mention that you saw him at breakfast, as if it were not a big thing, as if he might be with his boss, or something, so she will get the idea..