So I'm going to take a hypothetical situation with you and your wife as the co-stars!
Bob is a member of your social group. He senses that mrspod is not happy. He knows that your marriage isn't at the top of its game. He even has seen you with your secondary partner, and sees how much kinder and more loving you are to them. When he watches you and mrspod interact he senses tension.. From an outsider POV, Bob considers there is something off about your relationship.
He hears that you've been posting on a forum where you comment that mrspod is lazy, that you don't trust her, that you're apathetic about your relationship, that you're emotionally neglecting her. Now Bob is a counselor, and he's seen emotional abuse before. He is uncomfortable with the way you treat her, he doesn't think a healthy relationship should be like that, heís probably right.
Bob asks mrspod about your relationship. She doesn't directly answer his more pointed personal questions. She has stated to him that even though he doesn't see what she gets out of the relationship, it gives her X, Y and Z. He even asked mrspod's boyfriend about it. Her boyfriend thinks your dynamic is not ideal, but he didnít bring up any concerns about it being abuse and thinks Bob shouldnít pry any deeper than he has.
Nevertheless he feels mrspod is suffering from your actions. Even though she has shown no desire to discuss her marriage or confide in him, he feels that it may be more subtle than some cases, but that you are emotionally abusing her and he wants to help.
So what should Bob do?
The difference here is that you say she has volunteered that she GETS to feel inferior, gets off on the humiliation. If your wife actually has had sex in front of her, and didnít feel that anything there was off enough that she was concerned, I would guess no matter how squicky their dynamic is to you, she has chosen and even wants it.
So sure, tell her that you are concerned that she is being treated badly or whatever it is you want to tell her, say you are there if she ever wants to talk, and leave it at that.
OR you could directly tell her husband that you are uncomfortable with some of the public behaviors and talk to him about them. Maybe nobody has been brave enough to broach the subject, and if itís consensual humiliation, after realizing he is offending heíll go back to keeping it in private.
Happiness will never come to those who fail to appreciate what they already have.