Agree with everything you said JB, and I believe that EAs can be more dangerous than PAs.
With a "purely" PA, (not a "full-blown" A) there may be no feelings whatsoever involved-a one night stand would be the best example, but then the two move on.
But with an EA, the DS now has the toxic idea in their head that maybe they can do better than their spouse. Maybe the OM/OW can make them happier than the LS. And once that idea gets in their heads, they will never look at the LS in the same way again: the LS is now inadequate in their eyes, and they start to question everything about them-whether they are such a good person after all, whether they made a mistake by marrying them, whether they were really meant to be with someone else (usually the OM/OW), and then the DS starts falling into the "fog": their spouse is now a terrible person, they're ruining the DS's life, they're holding the DS back from their "true happiness", the OM/OW is a much better person than the LS will ever be...
Sorry if I rambled, but, even though I have never been cheated on, I still find this a compelling subject-hell, friends said I should have been a Marriage Counselor!
But, JB, I think your "questionnaire" could be summed up with one question:
"Would you feel very embarrassed/ashamed/ or 'caught' if your partner suddenly appeared behind you when you were with the OM/OW?"