In the Name of Allah (The Glorified and Exalted).
In Heaven (Paradise) every individual will be married. In the past in Arabia, some men practiced polygymy, had more than one wife. It was also the case that in other societies throughout the world people may have practiced polygyny or also had concubines or slept with prostitutes, because most men desired to have relations with attractive women other than their wives as well. Sometimes the wife at home was unhappy, and you know sometimes she just goes on strike, perhaps not enough money, love, etc, so men looked for relations in other places. In the nature of a man, having more than one woman is desired. Even among those that practice monogamy, many of these people had relations with others before they finally married. How many of these marriages are really "monogamous," when an individual lives in a promiscuous society and was in the previous habit of changing partners, is an entirely different debate.
In Islam, there are chaste maidens that occupy Heaven. They are humans. They nurture the infants and children that pass from this life and will wed the men that entire Heaven. Men will be married in Heaven whether that is to one woman or more, what the heart desires as it is said in the Qur'an about the rewards or life in Heaven, and the number is not limited to 40 (which to my knowledge I have never read or heard) or what some people have said of 72 women from Paradise. It may be less or more, whatever the Almighty Wills. He may increase the reward for whomever He Wills.
PS: I find the best way to learn about Islam is to read a lot of books, starting with the Qur'an and biography of the Prophet (peace and blessings of Allah be upon him) and then progressing, by learning the major theology such as belief in Allah, Purpose of Life, Angels, Previous Prophets, Day of Judgment, and Heaven and Hell. Then learn the rules and other parts of the religion such as religious practices.
I find the following sites helpful:
1) islamreligion (dot) com
2) thedeenshow (dot) com
3) islamqa (dot) com
And Allah (The Glorified and Exalted) Knows Best.