The reason that these are violations of God's law is because they have not proceeded from God but from the human heart. Matthew 15:19-20a "For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies: These are the things which defile a man" 

Adultery is the perversion of marriage.  There are many ways to pervert marriage.  Marriage is holy.  It is part of the the Church.  It is the basic unit of the Church.  To pervert the Church, Christ the Body, is a terrible thing.  The consequences are severe.  For those who are outside of the Kingdom of God, many of they cannot see this because it is part of the Kingdom of God.  It must be revealed and it is only revealed to those who have been born again.  To those who have been born again and still choose to pervert marriage, they remain infants in Christ and will not rule and reign in the Kingdom.  For this you know, that no fornicator, nor unclean person, nor covetous man, who is an idolater, has any inheritance in the kingdom of Christ and of God.  Ephesians 5:5  

Romans 1:32 Who knowing the judgment of God, that they which commit such things are worthy of death, not only do the same, but have pleasure in them that do them.

Hebrews 13:4  Marriage is honorable in all, and the [marriage] bed undefiled: but whoremongers and adulterers God will judge.

God blesses marriage, but terrible problems follow those who pervert those blessings that were meant for marriage.