I am under no illusions that her feelings for him may never go away and we will cross that bridge when we come to it, but I am hopeful that with that element out of the picture we can start mending (which we should have done in the first place without being so naive to think that this could have worked).
That's because she doesn't have a fundamental problem with cheating. Cheating on one's spouse is a legitimate choice in her decision tree. 
Some people, even some therapists, would have us believe that anyone might cheat if the circumstances are just so. But when you challenge that, when you really think about it... that's just not the case. Cheaters cheat because they're capable of doing the mental gymnastics to give themselves permission to do it. They've claimed one set of values, fidelity and honesty, and they CHOOSE to make loopholes. She vowed her loyalty to you, her faithfulness, but when she wanted more excitement in her life, suddenly she's "unattracted" to you and her fidelity no longer applies.
We either BELIEVE in the core values we claim or we don't. It's like being a "little bit" pregnant. You either are or you're not. It's a binary choice. We believe or we don't. There aren't escape clauses in our truest beliefs.
At the bottom line, your WW doesn't believe in fidelity. Her version of fidelity is one of convenience, one which serves her whims. That is, until it doesn't. Her version of fidelity has a "but..." in it. ie. "She believes in fidelity, but... not if she needs some thrills."
That's no belief at all. That's no fidelity at all. That's a person who is capable of twisting her espoused values to suit whatever arbitrary agenda occurs to her. And you know what?.. not unusual. Most of us really believe our own rhetoric on these kinds of issues because we haven't really challenged our own dogma. Life gets tough though, and the wheat has a way of getting sorted from the chaff though, doesn't it? And instead of dealing with that failure in values, the cheater rationalizes.
After having been down this road with my fWH with both EAs and then PAs a decade later (see profile page), I've spent A LOT of time mulling it over, and I am convinced that CHEATING IS ABOUT THE CHEATER. It's about character, integrity, the relationship between the values one claims and the actual deeds one chooses. And the cure is that the cheater has to do the painfully introspective work to realize that they were WRONG and that their integrity wasn't there, that whatever internal issues which have allowed them to twist up their espoused values must be fixed, that there is NO shared blame on that issue. They need remorse, empathy, boundaries, a new relationship with integrity, honor. It's a lot. And they can't do any of that when they're huddled up in sanctimonious belief that they were somehow justified in their perfidy.
Affairs are kind of like mirrors.. garbage in, garbage out. People don't engage in behaviors without some kind of payoff, right? It's not always straightforward, but the cheaters are negotiating with one another to get that payoff, and because these affairs seem to center on sex, we often assume that sex (or romance) is what it's all about. Figure though that if it was just about getting one's nut, neither of them needs someone else for that. So, it's more than that. It's about egos and attention, flattery, using another person to spackle in the voids inside, creating a new persona (or an old one), escapism, etc. None of it healthy and good. None of it really about the other cheater even. The feelings might seem intense and focused as if it were real love, but the AP is serving a function, papering over a shortcoming and a dearth of meaningful core values.
When the WS can't see the AP for the cheating scoundrel they are, it follows that they aren't seeing themselves as cheating scoundrels. No one likes to think of themselves in those terms. We all like to think we're otherwise nice people who have made some sticky choices or whatever. We don't like to think of ourselves as "bad people". This is just another rationalization though, another round of mental gymnastics. It is bad of us when we CHOOSE to do bad things. Your WW manipulated and coerced you into standing aside while she engaged in an action which has deeply wounded you and has threatened your family dynamic with destruction. She doesn't get to stand on the high ground and act like she's some stupendous example of honesty. She has corrupted "honesty" to get her own way.
It might be a trite old Dr. Philism, but "we can't fix what we won't acknowledge". Your WW is unlikely to see the badness of her AP until she's willing to see it in herself. That might be next week, next year, or even never. As long as she's telling herself she's an "honest" person, she's got no reason to really acknowledge the failures in her values system. As long as she can lie to herself about her own integrity and motives, she can continue to lie to herself about his. Garbage in, garbage out. While we don't want the WS shifting the blame entirely to the AP, we do need them to SEE "bad" values and "bad" character when they look there. As long as they still believe the AP is a lovely person though, they're not getting the mirror effect on their OWN behavior.
None of this is as simple as just her stopping cheating and you forgiving her. She has to actually have remorse for what she's put you through. Otherwise, try as you might, it's unlikely that you'll ever be truly satisfied with her again. Without real repair, resentment sets in and festers until it eventually destroys whatever love and affection you had left.
Rome wasn't built in a day, and I do think it's great advice to TAKE YOUR TIME. You will also do well to start making the kind of emotional investment in yourself that will strengthen you enough to insist on what you deserve. Life is short. Kids are grown before you know it, and unless we've built enough for ourselves, that empty nest can leave us bereft. I'm not saying not to put your kids first, just not to put them only. You matter. Your future matters. It's not a binary choice, us or them. We can act in ways that are good for them *and* good for us.
