After, they crash. They "wake up" from "being in a fog." They don't recognize themselves. They don't know how they could have done this, they frequently say "it felt like I was someone else."
Ok, Ima say it. This is nothing less than blameshifting. Rather than blameshift toward the other spouse, they blameshift toward "the fog".
"I was in a fog! It's like it wasn't me! I was in the clutches of the limerence and couldn't control myself. It was like I was possessed! I didn't recognize myself."
The theme here is appearing to take responsibility for the affair while at the same time lessening that responsibility by blaming "the fog". The reality is, if the mind was so addled they also wouldn't have been able to manage the logistics of having and concealing the affair. Hell, if they were so addled they couldn't understand what they were doing, couldn't understand the possible consequences, and couldn't control themselves, they'd be unable to manage driving, working, or tying their own shoes.
You know how there are some things you just don't say, even if they're true, because it's just too honest? Because, once it's said things change forever and not in a good way?
"Does this dress make my butt look big?" Very few people being asked this question are going to say "Well, yes. The cut, type, and color of that fabric just doesn't flatter your figure and you could stand to lose a few pounds."
In an infidelity situation, when asked "Why, how, did you allow yourself to do that to me? To us?" very few people are going to tell the flat out truth. "Because I really, really, wanted to and then it was just a matter of logistics."
But that explains why someone can think they are in "LOVE" with their AP, and then once they get caught they turn on a dime and now feel deep "LOVE" for their spouse.
Cheaters get something from their primary relationship. That's why they have affairs rather than end the primary relationship and date as a single person. They don't want to lose what they're getting from their primary relationship, but they also want whatever they will get from the affair. Once the affair is ended all they have left is the primary. Cue deep love for primary.