Setting aside the cheating---and I don't think you approve, reading your post, be it because of how he's treating her, or just the fact he has a wife and little kids at home (wayyy subtly obvious you don't approve, btw)...but setting that aside, the work dynamic is what is concerning me. I don't get from your post that she is in a position to harm your place within the company, but that doesn't mean it couldn't happen, depending on 'his' position combined with hers. I do agree with a previous post that she probably feels threatened by you because of your knowledge and while she may be throwing other friends 'in your face', I'd be willing to bet they have no knowledge to the extent you do, of her affair.

My advice, for what its worth, is not to explain to her that you'll 'be there' for her--you're under no obligation to do so at this point, and that's based on her treatment of YOU not on her treatment of her husband--just step back and maintain the 'cordial' relationship you have indicated you are doing now. The friendship HAS run it's course, and she's the one who ran it into the ground. It is not up to you to teach her she's wrong, by your actions. At this point, its only up to you to salvage whats left of your own self-esteem because she seems to have done a jolly job of stomping on that as much as stomping on her husbands because, fact is............when a man or woman is being cheated on...they KNOW it. They may not admit it right away, but for 99.9% of those cheated on...they KNOW it. If her husband is still hanging on....his self-esteem is swirling the toilet she's trying to flush you down.

Just put her into the 'acquaintance bin'...'friendly without commitment' etc. Refuse invitations out with her (if she bothers to ever ask again) because you have prior commitments. Refuse to be the sob shoulder she requires on occasion because you ARE the only one who REALLY knows...because you have prior commitments. Don't be rude. Just be distant.

She either will, or won't get her act together, but since you are not her keeper, or her mother, it is not up to you to get her to that place. That is up to her, and her 'adulterous partner'.

I'm sorry if I sound harsh. I've been where you are right now, and I would save you the confusion and ultimate hurt/betrayal when she decides to turn on you for 'knowing too much', and that could happen when the house of glass she's built for herself shatters, or if she just decides she can't take the added pressure of a 'tell tale heart' beating too close to her...which btw, might not even be her idea. She's listening to her AP drum now, darlin. Yours got lost in the forest of integrity.

Take care.