Well, Cain fixed that in Genesis 4:8 when he caught Abel feeding his livestock on Cain's crop in the field didn't he?
And Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him. And the LORD said unto Cain, Where is Abel thy brother? And he said, I know not: Am I my brother's keeper? And he said, What hast thou done? the voice of thy brother's blood crieth unto me from the ground. Gen 4:8-10
And the LORD not only blessed Cain with a wife, but a son and a city.
And Cain knew his wife; and she conceived, and bare Enoch: and he builded a city, and called the name of the city, after the name of his son, Enoch. Gen 4:17