Yes as a christian you should stand by her and try to concil her about what has happen and the serious problems she would cost for that family, try to lead her in the right direction explaining her down fall. We all make mistake in life and seek forgiveness.

It’s hard, but I don’t think it’s worth cancelling your friendship over. But I do think you should take a step back, especially if it’s making you this uncomfortable. “I know you’re a big girl and have the right to make your own decisions, but I don’t agree with this one. I’m willing to stay your friend, but I don’t want to meet him and I don’t want to get involved in your relationship with him until it’s over or he’s finalised his divorce.”

True friendship is like sound health; the value of it is seldom known until it be lost
http://twurl.nl/gu13c2

I think I’m with 10:09 Am on this one. I would feel obliged to tell my friend I’m not comfortable with her involvement (if I don’t tell her, my feelings will probably sneak up behind me and bite both of us in the backside.) After that, it’s up to her what she wants to do about it.

Yes, you withdraw from the friendship; you “cancel” it.
(Sorry about the amateur psychologizing, but) I would say that what’s really bothering you about this situation is that you’ve learned that *you* can’t trust your friend. Since she puts her own feeling good above what you consider to be core moral principles held to by every decent person, you can no longer trust her to ‘have your back’ in any situation where you might need and expect her to do something hard, something that makes her uncomfortable (but is *right*), to support you.
How, for instance, can you possibly trust her around your own husband, now? (You can surely trust him, but not her.)
You owe it to her to tell her how you feel, but not to have any contact with her after that.
Anyone that suggests otherwise, by the way, is engaging in a kind of compartmentalization that the human psyche just doesn’t support.

ethics is not about judging or preaching to others, but about being true to the standards you live by. If you have principles that posit: 1) I’m complicit in any evil I’m silent about; 2) sex with another person’s spouse is wrong; 3) complicity in destroying my boss’s marriage is wrong; 4) I take on the moral aroma of the people I associate with, you have no right to pass judgment on the adulteress, and no right to be her priest unless you’ve already established that role. You have an obligation to yourself to refrain from swimming in what you identify as filth.

I don’t think =she’s= done anything morally wrong. She has no obligation to this man’s wife, HE does. What she’s done is simply stupid, attaching herself to a cheater – and one with power over her career.
But yeah, there’s no good way out of it, because these women simply don’t hear it when you tell them that a man who cheats once cheats twice and the very fact that he’s in a relationship with her at all is indicative of his poor character and insufficiency as a prospective partner.

I can’t tell you what to do or think. In your place I would remain friends, I would express my disappointment, and make it as clear as I could that I would not aid and abet this relationship in any way, shape or form. And -when- it falls apart, as the smart money will bet it will, she’d best be ready for lots of I told you so’s as well as comfort.
As for the wife, I have no idea what their relationship is, or their agreements are. She might know but doesn’t want to be forced to face it. She might know but is willing to live with it for the ‘sake of the children’. Right or wrong, they have their stuff and I’m not going to butt in, unless I see something illegal happening. Adultery and stupidity are not illegal. Our politicians have seen to that.

Oh my heavens, what a sheltered life folks must lead. Among our circle, my wife and I are usually around married people who are dating people whom they are not married to. If we worried about that sort of thing we would not have any friends at all.