How so? And who took advantage of her the other times? The problem was there before he ever entered the picture. However, now that he's in your M, it compounds the problem. What has been decided about the foursome friendship? What has been decided about the A?
This friendship the four of you have had is over. His W deserves to know why. Your W should be the one to explain to her friend that she was betrayed, but i doubt she will. I think he should tell his W. It won't save the M, but neither will keeping it hid and pretending everything is still the same between the four of you. Your W and the OM has destroyed the friendship, not whether or not you inform the other W.
I may not be able to tell you what will work to save your M, but I think I can tell you what won't work..........and this behavior from you isn't working. I personally believe women grow dissatisfied when their emotional or physical needs are not met by her H. But there is another one........loss of attraction.
It seems just today I have posted about that subject a lot. It amazes me how the H can't tell, but I suppose I can understand to a point.......knowing how women conceal those feelings so much. However, it comes out in other ways, usually her saying she's not in love with him anymore and has felt unhappy for a long time. She might as well say, IDLY so I'm not responsible for my actions (like turning to another man), and in most cases, she already has OM she's watching.
There was something missing in the MR for her that you didn't see. Spending quality time together, sharing your soul with each other, keeping the romance alive, having fun times, etc. are so important to women. But if she started feeling less attracted to you b/c of whatever reason.....then disrespect would soon follow. B/c a woman will put up with a lot of stuff if she's attracted to the guy.
Just as it is important to the man to be admired, it is important to her to feel the admiration. I believe a woman pushes undesirable feelings down within herself. She will experience sadness, unfulfilled, a lot of resentment, and other negative feelings she knows she shouldn't have if she were happy. It will eventually take over and turn into something very close to disgust......and finally just an emptiness. She can't feel in love with her H!
So you need to start with some basics by becoming a man who can be admirred/respected. Not just as some type of pleaser for her, but for your own self-confidence. You do what you can do to improve yourself, and therefore the chances for attraction, and the rest is up to her.....in that area. You can't force her to feel what she doesn't.
Physical appearance is important, of course, but for women it is lower on the list than for men. Other things about the male is what attracts her. Mostly his manliness and take charge attitude. Any time he starts showing signs that resemble a female, it kind of sets her back. I mean, yes we say we want a sensitive man who will understand how we feel......but at the end of the day, we want the mister and not a sister.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!