(Proverbs 5:15 KJV) Drink waters out of thine own cistern, and running waters out of thine own well.
Modern Americans are generally ignorant of “cisterns” (953a). Before the days of indoor plumbing water was always a problem. You might get a lot of rain for half the year but nothing the other half. Streams could dry up. In some areas wells were impossible to dig but most people could dig a pit, which is the basic meaning of the Hebrew word. I was listening to a TV program about houses in Central America that had cisterns holding enough water for a family of four for a year. The modern equivalent might be the water towers that you see above many towns as you drive across the country.
This is a metaphor about being faithful in marriage. Each person is to have their own sustaining relationship with one other person. We used to call people butterfly when they went from relationship to relationship. We are supposed to be buckets connected to one source.
So? God’s plan is one man and one woman, for life. This is just another expression of it.