You may as well ask how faithful humans are these days.
This has not always been the case though. Do you know of Jane Austen, Nevuela? Have you ever read her novel Pride and Prejudice?
What was the dilemma of the Bennet family? --Five daughters, no sons. Since British women in the early 19th century could not inherit property, the estate would pass to the nearest male relative upon the death of Mr. Bennet and the girls would likely be turned out on the street.
When a women is utterly dependent upon a man for her material needs, her loyalty (In the form of fidelity) becomes extremely important, as the repercussions of disloyalty are simply too severe.
As that economic shackle has been lifted, women have gained greater freedom, both for good and for bad.