The way you have worded it makes it sound like you have put all the blame on women for having affairs ("women have affairs to..."). It takes two to tango, so to speak. In fact, according to wikipedia, men are significantly more likely to have an affair than women (http://en.m.wikipedia.org/wiki/Infidelity).

The fact that men are often actively trying to get in women's pants likely has a greater effect on these statistics than women's genes' desire to reproduce.