I am a Theology student at VUU, a student asked this question, I am seeking info.
Answers (3)
There's a few theories on this, so I'll give you the main 3 (and able never married):
1) Cain just married one of adam and eve's other children (probably the most plausible explanation, kinda weird but incest was common back then)
2) They married angels. They'res some vague mentions of the "children of god" coming down and living with the men on earth. Could have just visited, but some believe they had kids with people
3) Probably the least common theory, God created a wife for Cain.
These are all just theories, the bible never gives a definite answer on this. I hope I helped!
Genesis chapters 3 and 4 present the following information: (1) Eve was “the mother of everyone living.” (2) Time elapsed between the birth of Cain and his offering the sacrifice that was rejected by God. (3) Following his banishment to become “a wanderer and a fugitive,” Cain worried that ‘anyone finding him’ might try to kill him. (4) God set up a sign to protect Cain, indicating that either his siblings or other relatives might try to kill him. (5) “Afterward,” Cain had intercourse with his wife in “the land of Fugitiveness.”—Genesis 3:20; 4:3, 12, 14-17.
From the above, we can rightly conclude that Cain’s wife was a descendant of Eve born on an unknown date. Genesis 5:4 acknowledges that during his 930 years of life, Adam “became father to sons and daughters.” Of course, the Bible does not specify that Cain’s wife was Eve’s daughter. Indeed, the fact that she is mentioned after Cain’s banishment indicates that enough time had passed that she could even have been one of Adam and Eve’s granddaughters. Hence, The Amplified Old Testament describes Cain’s wife simply as “one of Adam’s offspring.”
That Cain married his sister or a later female descendant of Adam through the marriage of any of Adam’s sons or daughters is viewed by some societies today as unthinkable. This is usually because of societal taboos or fear of genetic defects.
Also, it is noteworthy that it was not until Moses received God’s laws for the nation of Israel in 1513 B.C.E. that intercourse between such close relatives was specifically forbidden.—Leviticus 18:9, 17, 24.
Today, we are millenniums away from the perfection once possessed by our original parents. The effect that genetics and heredity have on us might not have been a factor for them.
First, it's ok to admit you don't know something. It is a disgrace to pretend you know something when you don't. When you ask strangers to tell you what the bible says or what it means, you either get something they heard from somebody else, or you get something they made up so they wouldn't have to admit they don't know.
The bible does not mention Cain's wife, but it does mention that Eve was the mother of all mankind. So Cain married a sister or a niece. Marriage to sisters or half sisters was common in the early years, and marriage to cousins is common to this day.