We are very different from our closest relatives, chimpanzees. Everywhere in the world, we form pair bonds, extended social and sexual relationships. A female chimpanzee comes into oestrus in the middle of the month, and copulates with almost every male except her own sons. They are promiscuous, and they raise their children by themselves. They don't form a pair bond and raise their children as a team.
Human beings tend to divorce during around the fourth year of marriage.
Everywhere I've looked, in 20 societies, everywhere in the world where women have some economic independence, the divorce rate is high, because both men and women can leave a bad relationship when they can afford to go. What's interesting is that the vast majority of men and women remarry and try their luck again. Many many changes in technology affect our love lives. For example, women are having far fewer children, so they have more time to get an education, and move into the work force, and have careers, and pick different kinds of partners. They can travel to different countries, and different cities, for business, and meet different kinds of people.