II Sameul 5:13 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 Samuel 5:13 says (NASB):

"Meanwhile David took more concubines and wives from Jerusalem, after he came from Hebron; and more sons and daughters were born to David."

Everything in the Bible is true. This is a true account of what David 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.