It was neve meant to be one man and one woman together forever.
If you go way back in history men hung out with men and women hung out with women and they came together for the purpose of making children.
The problem with most marriages, with the possible exception of a few, is that people tend to grow in dfferent directions and tastes tend to change over time. A man who likes a curvy woman with large breasts today may end up like a thin woman ten years from now. And couples sometimes lose interest in constantly having sex with the same person.
A woman may do things to a man to please him and get him to marry her then after a while she may no longer do those things that made him happy in the beginning.
In summary, people change with time and it was never really meant to be one man with one woman for all time.
