II Chronicles 11: 21 is a historical account of part of David's life. There is nothing in this passage, or anywhere in the Bible, that says it is acceptable to God for us to have multiple wives and concubines. Unlike Leviticus 18:22, which is a direct command from God, these passages only describe what happened.

This is what II Chronicles 11:21 says (NASB):

"Rehoboam loved Maacah the daughter of Absalom more than all his other wives and concubines. For he had taken eighteen wives and sixty concubines and fathered twenty-eight sons and sixty daughters."

Everything in the Bible is true. This is a true account of what Rehoboam did. However, not everything in the Bible is intended as an example for us to follow. The people in the Bible were ordinary people (except for Jesus) who, like us, were not perfect.

We might point out that Rehoboam, the son of King Solomon, was not a good king. For example, as a result of his actions the Bibles says:

"So Israel has been in rebellion against the house of David to this day." - 2 Chronicles 10:19

Remember, the the Old Testament says that the line of kings coming from David would go on forever and the Savior would be of the line of David. So the house of David was very important. And David's grandson, Rehoboam, managed to turn all of Israel against the house of David. He was not a good king, nor a good example for us to follow.