Family Code § 4323
CHAPTER 2. Factors to be Considered in Ordering Support
(a) (1) Except as otherwise agreed to by the parties in writing, there is a rebuttable presumption, affecting the burden of proof, of decreased need for spousal support if the supported party is cohabiting with a nonmarital partner. Upon a determination that circumstances have changed, the court may modify or terminate the spousal support as provided for in Chapter 6 (commencing with Section 3650) of Part 1.
(2) Holding oneself out to be the spouse of the person with whom one is cohabiting is not necessary to constitute cohabitation as the term is used in this subdivision.
(b) The income of a supporting spouse’s subsequent spouse or nonmarital partner shall not be considered when determining or modifying spousal support.
(c) Nothing in this section precludes later modification or termination of spousal support on proof of change of circumstances.