So if one woman is up for an affair this disproves my supposition that the majority of women are against affairs, that is a long stretch.
As for the mumsnet thing they have a lively political forum which my partner sometimes contributes to and from that point I have perused other parts of the site, the relationship forum is an eyeopener.
The point is that it is just that - a supposition. There isn't anything unusual about a woman in a sexually unfulfilling marriage wanting an affair. Or indeed a woman in a happy marriage. I find it difficult to believe that you know only women with one narrow view or set of experiences, so I think it more likely that you are projecting a particular viewpoint onto women as a category.