Cohabitation and Alimony

My husband and I have been paying his ex-wife alimony for 17 years and we have reason to believe she is cohabitating. What exactly do we need in order to prove she is? In doing so, is that grounds for terminating alimony?

If you can prove she is living with someone in a romantic relationship your husband can make a motion to terminate alimony on those grounds. Many people prove co-habitation by hiring a private investigator to obtain photographic evidence of the payee ex-spouse or paramour entering and exiting the home in the morning and at night.