Is it true that there is polygamy in the celestial kingdom because it is a heavenly law, and that people will have to live it then? If so, why does the Church teach us monogamy?
There have been times in the history of the world in which polygamy was the accepted form of marriage arrangement. Abraham, Jacob, Moses, and a number of other ancient prophets practiced polygamy. But remember that they did so because they were allowed by strict commandment from the Lord (D&C 132:37-39). Then, during other times in history the Lord specifically prohibited such marriage arrangements (Jacob 2:27-30).
In the beginning of our dispensation the Lord once again revealed the law of plural marriage to the Prophet Joseph Smith as part of the restoration of all things (D&C 132:40). Later, this law was revoked under President Wilford Woodruff (Official Declaration 1). Since then, no member of the Church has been justified in teaching that couples currently living on the earth will have to adopt polygamy in the distant future. The living prophets have not taught this.
So, those who lived in ancient times under polygamous marriages and lived righteous lives will inherit the celestial kingdom and will have all their spouses with them. Those who did not live under polygamy will not have to adopt it.
Anyone who understands why the Lord gave this law in ages past would also understand the heavy responsibilities associated with the same. Unfortunately, I have encountered some people interested in this doctrine for the wrong reasons. For those in that category, I would suggest that they prove themselves worthy of having one spouse before thinking about having more than one.