"Unstable relationships" means that the relationships are not steady or consistent, and they may have frequent conflicts, breakups, or changes. Full definition
An animal that has been confined during this stage in its development or that has had unstable relationships with people during this time may develop undesirable behavior. (homevet.com)
I was in a very unstable relationship which ended after 6 years - and there was a lot of «moving on» that had to be done. (girlmeetsbowblog.com)
More education sharply reduces the drifting into unstable relationships and the single parenthood that this often produces. (educationnext.org)