In the institution of marriage established by God as a lifelong, exclusive relationship between a man and a woman.

Genesis 1:27
So God created mankind in his own image, in the image of God he created them; male and female he

created them.

Genesis 2:24
That is why a man leaves his father and mother and is united to his wife, and they become one flesh.

Matthew 19:4-6
Haven’t you read,” he replied, “that at the beginning the Creator ‘made them male and female, and said, ‘For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh. So they are no longer two, but one flesh. Therefore what God has joined together, let no one separate.