Genesis 4:19

“Lamech married two women, one named Adah and the other Zillah.”  Genesis 4:19

Lamech, Cain’s great, great, great grandson, is the first recorded instance of polygamy.  It doesn’t give any indication of what God thought of this – only that it happened.  Was this something that one man decided was a good idea, rationalizing his wandering eyes?  Did God approve of it or just allow it?  So far the only mention God has made to relationships was back in Genesis 2:18 when he said, “I will make a helper as his partner,” and then in chapter 3 he tells Eve, “Your desire will be for your husband, and he will rule over you.”

Any mention before this always indicated one man and one woman.  “For this reason a man will leave his father and mother and will pursue his wife, and they will become one flesh.” Genesis 2:24

Genesis 4:18

“To Enoch was born Irad, and Irad was the father of Mehujael, and Mehujael was the father of Methushael, and Methushael was the father of Lamech.”  Genesis 4:18

So Cain became a grandfather and then a great grandfather and his line went on.  Despite his murder of his brother, God allowed him to have a family.  They had some interesting names.  Irad means "fugitive," Mehujael means "smitten of God," and Methushael means "man who is of God."  The meaning of Lamech is unknown.

Genesis 4:17

"Cain made love to his wife, and she became pregnant and gave birth to Enoch.  Cain was then building a city, and he named it after his son Enoch.” Genesis 4:17

So if Cain was a restless wanderer how did he build a city?  Back in verse 12, God told Cain that the ground would no longer yield crops for him and he would be a restless wanderer on the earth.  It doesn't sound like this was temporary punishment.  One translator argues that end of verse 12 should actually read, "with dire calamity and fear you will exist upon the earth."  So Cain built the city in an effort to protect himself.  

He named his son and the city Enoch which means "dedicated."  One can only speculate about what he was dedicating his son and this new city to.  Was it God?  Was it safety?  At this point there is no evidence whether Cain continued his life in conflict with God or if he turned to to God for the remainder of his time on Earth.  He talked to God, so he would have a hard time denying the Almighty's existence, but just because you believe something exists doesn't mean you accept it's authority over your life.  Only God knows which Cain choose.