“Contrary to what many people believe, when an ex-spouse cohabits with a romantic partner, the law does not provide that spousal support paid by the ex-spouse will be terminated. Instead, there is a rebuttable presumption, affecting the burden of proof, that the support ex-spouse has a decreased need for spousal support. This means that the support spouse has the burden to prove by a preponderance of the evidence that his or her need for spousal support has not decreased. The supported ex-spouse does not have to be holding himself or herself out as a spouse of the person that he or she is living with in order for the court to find a decreased need. If the court determines that the circumstances of the supported ex-spouse have changed, the court may modify or terminate the spousal support paid to the supported ex-spouse.”
[LW Greenberg, California Family Law]