I wanted to add this as my H is home, rebuilding, and with (almost) no contact with OW.
I think H would still claim this was never an EA, and that I had got it wrong. The fact that (a) it never went physical and (b)the fact that there was never a mutual exchange of "I love you" justifies this in his mind.
I regard it as an EA because of H's obsession with her, constantly emailing and texting her, saying "I could fall in love with you/ you get my libido going"; suggesting holidays (which luckily they never went on); the idea that they had something special between them, a mutual empathy that surpassed love; lying to me to go out with her to the cinema, concerts, theatre, dinners, etc... (which he justified on the grounds that I was just too unreasonable...)
Everyone said it would probably go physical, but it didn't (I think she liked his attention, but never intended to have a fling with him). I'm glad that it didn't go physical, and that they didn't live together/ go on holiday together, etc, because it makes reconciliation easier (and it's hard enough). But on the other hand, I think he still considers her as a wonderful person, and seems unable to conciliate how he sees her with how she behaves (telling him she was afraid of me, telling her mum I'd threatened her, etc.) So he refuses to address the issue. As far as he is concerned, he did no wrong, she did no wrong and I am unreasonable for getting angry, which must be because of my own insecurities... (I mean normal women wouldn't mind this at all, would they?)
So... EAs are a fantasy, an escape; yes, physical attraction and infatuation are involved, which diminishes with time, but it's more than that. It's about escaping their lives, their routines and the inevitabilities of existence; of something new and exciting to escape the humdrum. H always acted like it was nothing to do with me, and in a way he's right. He didn't do it to punish me, I just didn't figure in the picture. I was part of the scenery, and just didn't count.
It's hard to forgive someone who doesn't admit that their actions were wrong.