bt,
I'm Schoolbus. Not a psychologist, but that's certainly part of my educational background.
I have friends who are psychologists

Here would be some questions I would ask, if I were a polygrapher, and I've worked with them, too. (Gee, I get around, don't I?)
I've asked my H some pretty specific questions, because he was a guy who believed in the trickle-truth method of confession.
1. Did any part of your genitalia touch any part of the other woman's physical body, either through clothing or direct skin-to-skin contact?
Now that one is pretty specific, doncha know?
2. Did any part of OW's body, above or below the waist, touch any part of your body, either through clothing or direct skin-to-skin contact?
3. Did any part of your body or her body become sexually aroused during any encounter between the two of you?
4. Are you emotionally attracted to OW?
5. Are you sexually attracted to OW?
See, I've covered LOTS of ground here. tons.
No weasel room. Either he touched her or he didn't, and we have no wiggle room for oral sex, hugging, casual hugging, hair being brushed back from the face, NOTHING. Either they touched or NOT.
We can go for details after the poly - on what touched or did not touch, and why.
And then we can talk about why there was sexual arousal.
Can't really weasel out of it. Either they touched, or not.
Either he is emotionally or sexually attracted, or not.
He will pass or fail.
IMHO, you are being gaslighted. Your husband and this woman have had a physical affair - of some sort, and he failed the polygraph because of it.
You need to talk to the OW's ex-husband and find out what happened to cause their divorce. That advice is very sound - do not skip this step.
One of the most important things you are missing here is that you need to understand that your husband
LIES TO YOU.
The polygraph PROVES HE IS A LIAR.
Wayward spouses LIE.
He has already lied to you for YEARS. There is no motivation for him to STOP.......
Why would he now tell you that he has had a physical affair, after you have believed the story about it being "just an emotional affair"??????
He has sold you a bill of goods. You bought it.
He has no motivation to change the story, except any motivation that YOU put into place.
Motivate him using the MB plans of Plan A first,
a good re-exposure of the ONGOING AFFAIR that you discover using your spying techniques (I would use a good program to undelete all of the deleted emails, by the way)
and then look at planning a good Plan B.
And do not, for one moment, believe that this was an EA.
Nope.