I'm a WS and I want to chime in here just a bit. My childhood was spent in an abusive (physically, mentally, sexually, bullied, demeaned, raised by a narcissistic Mother and a sadistic brother ), neglectful (I was never protected from my abusers, in fact, it was made clear that I deserved it. I was made to apologize to my childhood rapist for "lying" about him raping me) and loss-filled (At 16, I lost my father, my uncle, my dog and my girlfriend within 3 months, failed school, and was told that my father dying wasn't a reason to not get my homework in on time) childhood. There wasn't anyone in my life that told me that I was a good person, that I deserved joy and success and happiness in my life. My life was meaningless, and so my only value and source of happiness was to do my job, which was to make others happy and make them feel worthy and whole. It ultimately was a large factor in the how/why of my affair.
I had no self-love, in fact, I really had no "self". Shortly (6 months?) before my affair began, I had a mental breakdown from having compartmentalized all that abuse for all those (49) years. I was later diagnosed with Complex PTSD, depression, anxiety, a condition similar to DID (multiple personalities, resulting from the abuse) and showed signs of borderline disorder (and while undiagnosed, I'm convinced I have ADD). At the end of the day, whereas most emotionally healthy people have a sense of self, of purpose, of worth, of integrity... I had a complete lack of all of those things.
I derived my value, as a human, as a father/husband/friend/family/co-worker/neighbor, by the praise and approval that others gave me. As long as I was being praised and liked and loved, I was okay. Knowing I was valuable to others made me feel special, and whole, and worth something. So I spent every second of every day being as wonderful as I could. I was the smart one, the funny one, the talented one, and everyone loved me because I worked hard to "hustle for my worth" (to quote Brene Brown).
But you know what happens when you derive your entire self-worth from others, and then, one day, that "stream of love" stops coming in? You fall apart. It feels as if someone cut off your oxygen and you can't breathe. Worse than that, lacking any praise or love from others, you are left with nothing but "voices/messages" that your wife mentioned. As you said, not actual voices as in "call the guys with the straight-jacket" sort of way, but constant thoughts of how horrible, useless, stupid, and unloved you are. It's a pain that reaches deep into your soul, and it is ugly, and evil, and full of lies and stories that you end up telling yourself, lies and stories that say that you are worthless, and using up food and oxygen that someone better than you could be using. I assume that in many ways, it is similar to how a BS feels comes D-day. It's that feeling of non-stop pain, loss, self-doubt. It's almost impossible to quiet that noise in your head that makes you suffer. A healthy person will dig deep inside themselves and remind themselves that they are worthy of better, of more. They will love themselves, and don't require anyone else to do so in order to know their value in the world. For a WS however, especially someone with a background similar to mine, we lack the skills to soothe and support ourselves. We don't know even know it exists as a possibility. The tools we have are based on survival, not thriving, not living.
At some point, the WS figures out that if they aren't getting the external praise and support they need, then they have to go get it. Maybe they go looking for it on their own, maybe it finds them. Either way, the minute someone else starts to feed them praise and appreciation, well, it's like giving a man that is lost in the desert a glass of water. It becomes all he think of, all he needs, and what would be a simple glass of water to anyone else becomes his entire reason, and ability, to survive. The fact that he has barrels of water at home doesn't mean anything because, either for real or in his mind, those barrels aren't available to him. This glass of water is however. We can argue all day long about whether that is "true" or even "rational" and it is probably neither, but what IS true is that the WS's mind sees it that way because it needs to see it that way. Otherwise, we're horrible people, not just for cheating, but just for existing.
To take things one step further, imagine taking that glass of water away from the thirsty man, and then driving him far out into the desert and leaving him there, with the clear message that drinking someone else's water was wrong. What now? He gets desperate. He gets angry. He gets defensive. He makes up stories about how it is others people's fault that he ended up like this so that he doesn't have to blame himself. And one of two things happens. Either he gets locked in the self-story that says he's the victim here, and goes off to find anyone that will share their water with them, or they dig deep, find some kernel of a reason to keep on existing and growing, and learn to find enough water for themselves to get out of the desert alive.
I am in year 7 of recovery. After many, many years of therapy, while I cannot say I have the love for myself that people such as yourself and my wife do, I do now have the ability to see my own value, to survive without relying on others for worth, and have a deep understanding of why I act and feel like I do, so that I can make choices and decisions that allow me to live a better life, and to love myself a little more each day. But I realize I'm "lucky". For every person like me, there are a hundred, maybe a thousand, that can't reprogram that brainwashing that trauma did to them. It's hard, it's painful, and it takes more effort and courage and a willingness to fail than I can even put into words.
One last thing. I think it is wonderful that you are exploring this aspect of your wife, just be careful. I can tell you that, from my own experience, it's very easy for someone like that to try and excuse it away. It turns the camera back on her and her pain, which can be a catalyst for you to show her love and remind her of her worth... things she desperately needs. But as you know, WS's are selfish and "all about themselves", so being supportive to her, comes with a high risk. The idea is to give her support, but not get lost in it, not get sucked into it, and to allow her to use your support as a complete replacement for her own. She needs to feel the hurt, and work through the pain. She needs to dig deep with a professional if possible, because if she doesn't understand herself, then she can't do/be better in the future. It's a tightrope to be sure. I know my wife's support and love helped me immeasurably. But it also hurt her just as much, as it delayed my ability to show empathy and compassion for her.
Best of luck to you.