You really have the right instincts already and are doing a great job! Like you, I don't get the saving face thing, at least completely. I think more out loud truth helps everyone. But since not everyone feels that way, it doesn't work for everyone. But if this is critical to HER, it may explain why she can't admit an affair, assuming that if it looks like an affair, it is an affair. At least you're pretty smart about that. But she may never be able to admit it, keep that in mind--if she faces that, she might not be able to face you again.
If you haven't bought Divorce Busting yet, buy Divorce Remedy instead, it's the upgraded version. Keeping Love Alive audios and the new video version of the Last Resort Technique are wonderful as well. If you only want one, go with Divorce Remedy.
If she brings up divorce, be calm and matter of fact and move on. Not snippy, no argumentative. Just don't discuss it. It will only go poorly. It's ok to let her sulk or cry etc. If she wants to talk about other things, really listen. Watch her body language, tone, etc. Really pay attention. But if she goes off on you and you can't bring her gently to calm conversation, gently end the discussion.
And take good care of yourself.
sg Love is PATIENT, love is KIND, LOVE never fails / DB since 2001