Legal Question in Family Law in California

No that's not a valid reason

I disagre with Mr. Kiani. It depends on the terminating conditions of the spousal support order. If it terminated upon you cohabiting with someone, it may end.

"Seeing someone" is too vague to give a reliable answer. Mr. Roach presumes it means "co-habitating." Personally I have always been "seeing" someone for a very long time before co-habitating. The bottom line is that the specifics of the relationship have to be compared to the language of the support order before an accurate answer can be given. In any case, however, unless the order or judgment has an automatic terminating clause for remarriage or co-habitation, your ex would still be in contempt of court if he fails to keep paying until he makes a motion and gets an order terminating support, even if he is entitled to the terminating order under the existing support order.