If the ‘other man’ gets attached he will inevitably at some point start needing more from the married woman. My heart goes out to him more than any one else in this arrangement because he is usually the one who gets disturbed first and has more to lose.
He may start thinking about asking her to leave her husband. He could be thrown out of the triangle and the married couple could end up fixing their relationship, this could happen.
In some instances he ‘knows’ his wife is cheating on him and looks the other way.
In other instances his defenses are so thick he doesn’t read the signs at least consciously.
Personally, I think most if not all married people know on some level if a spouse is cheating, but that’s just my belief.
Instead, defensive stuff happens like distancing from each other or finding another lover to make up for what is not happening in the marriage.
The problem is you can’t get a piece of what you need from one person and another piece from someone else and expect to have a stable and satisfying love life.