when a spouse, girlfriend/boyfriend/husband/wife is the greatest partener around when the relationship is fun and easy going. When things turn for the worst or become difficult, as relationships eventually do, they jump ship like their pants are on fire.
P1: Why did Melissa want that divorce after being married for so long? They seemed to be happy...
P2: She is a Fair-weather Spouse...
P1: Oh, makes sense, Bitch.