Well among my female nursing friends/acquaintances/colleagues, all now in their late forties early fifties,I can think of about twelve who have cheated on their dp, were never found out, and are still with their dp.
Only one has split from her husband, and that was for other reasons, and her affair was not discovered.
From conversations with them, and with clients I have counselled in the past, there are many women who want extra marital sex in the same way that many men do (please not I am not saying ALL men or ALL women), and don't want to split up the family or leave their partner.
To go along with the cliché I think women who have affairs tend not to be discovered/leave clues in the same way men tend to.
Reasons given were boredom with hubby, husband's sex drive disappeared, curiosity, wanted attention,wanted to try someone else after years of same man, just feeling horny and saw opportunity.
Another thing I have noticed is the number of older women whose sex drive increased as their husband's tailed off; I think we read a lot on here about women being pestered (especially after childbirth) for sex, but there are a lot of women out there who want a lot more sex than they are getting, and still feel confused and a bit ashamed/astonished at their need for sex.