God made man and named him Adam. He decided that Adam needed a helpmate, so he made woman and she was named Eve. Adam and Eve were the 'perfect couple', until Eve was deceived in the Garden of Eden.
Then, when Adam also ate of the forbidden fruit, they realized they were naked. They had sinned against God. Marriage is to be a covenant between two people who are faithful in their relationiship with one another.
Genesis 2:18 And the LORD God said, It is not good that the man should be alone; I will make him an help meet for him.
Matthew 19:4 And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female, Matthew 19:6 Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.