Is she most likely lying about her opinion of our sex life just before and during her affair?
You've provided almost zero detail about your WW, her A, your marriage, how the A was discovered, etc. We have very little to base an inference from.
Affairs are motivated by a wide range of things, but I think that in most cases it boils down to the WW feeling dissatisfied in some aspect of her marriage. She perceives her emotional needs aren't being met (very common), or she feels a haunting sense of inadequacy or being neglected. Etc.
In many cases, we see BH's surprised about the relatively low level of physical attraction possessed by the AP. He was old/fat/out of shape, etc. The vector is clear: he was providing the positive reinforcement she craved, which led her to reward that with sex.
In your case, what we do know about the A doesn't fit that pattern. We often hear about WH's having sex with a younger, fitter, bustier woman. As men, we can understand the male attraction to that at a visceral level, even if most of us would not consider cheating on our wives just for some young, hot strange.
Your WW did that, however. She cheated on you for some young, hot strange. That's isn't a common occurrence here on SI. I think you have inferred that she did it because she found him sexually irresistible, which is reinforced by the fact that she had sex with him repeatedly and exhibited a high degree of sexual brio with him.
We don't have a lot of other detail of your thread to work with, but based solely on what you have told us, I think you're right. I think she found the AP to be a tasty piece of manmeat and she wanted sex with him more than she wanted to honor her wedding vows to you. She made that choice, on purpose, for that reason.
No matter what she tells you about your sex life with her, as long as you stay married to her, you'll have to live daily with the reality that she decided that sex with the AP was something she craved strongly enough that she was willing to end your marriage to get it.
Here is another way to state that logic. Every cheater must, fundamentally, cross that line. Make that initial decision of violate his/her wedding vows and betray his/her spouse. It's a big deal for most people.
In many cases of cheating, we learn that the cheater was driven be a sense of something akin to despair, a feeling that the marriage was broken.
I've not heard you say that your WW expressed any version of this to you. In fact, in this thread, she's telling you that everything in the marriage was fine.
So, logically then, what would be the force that motivated your WW to cross that line. The only conceivable force would be an overwhelming desire for sex with this Adonis, strong enough to justify betraying you.
[This message edited by Butforthegrace at 8:55 AM, April 10th (Saturday)]