to leave your husband, wife, partner, etc. in order to have a relationship with sb else :
He went off with his best friend's wife.
to leave your husband, wife, partner, etc. in order to have a relationship with sb else :
He went off with his best friend's wife.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005