There are precious few women who'll put up with being some married guy's dirty little secret for absolutely NO payoff whatsoever. Why would they waste their time with some cold, rotten, unemotional and unaffectionate guy?
It seems impossible. I would have thought it was impossible, but it turns out there are plenty of women like this.
Here are some reasons why OW would be that desperate:
She is too messed-up to attract a normal guy and will take whatever she can get.
She grew up abused and unwanted, and has an intense fear of being alone and/or abandoned.
She has never been with a healthy guy, so has no idea what real affection or desire looks and feels like.
She isn't capable of true intimacy or warmth (personality disorder), so the drama and intensity of an adultery is her substitute.
She has no self-worth and doesn't expect WH to value her either.
In our case, OW literally blackmailed fWH into sex at the end. She threatened to tell me or his work colleagues if he stopped. We're talking mechanical, missionary sex with no stimulation or O for her. Who would want that? But when the NC letter came, OW threatened suicide.
Our MC told us that this is more common than you would think. These OW's will hang on to a man, any man, by any means . . .
People involved in affairs are to some degree mentally unhealthy. In our case, the degree was high!