It is nearly impossible to steer clear of casual sex when you are stressed out and frustrated. Especially when the opportunity presents itself. I've hooked up with some of the dirtiest bar girls ever, ignoring all the precautions I have to take. Same goes for taking drugs and alcohol.
Nature is stronger/smarter than any of our designs to deceive it imho.
Yes, true, and even when she was with her husband, it sounded like he didn't really know how to make her feel good so all that pent up energy would be really needing to go somewhere.