Jamieson, Fausset and Brown on 2 Samuel 20:3

3. the king took the ten women his concubines--Jewish writers say that the widowed queens of Hebrew monarchs were not allowed to marry again but were obliged to pass the rest of their lives in strict seclusion. David treated his concubines in the same manner after the outrage committed on them by Absalom. They were not divorced, for they were guiltless; but they were no longer publicly recognized as his wives; nor was their confinement to a sequestered life a very heavy doom, in a region where women have never been accustomed to go much abroad.