In my 30 years in corporate life I've seen all kinds of "work wife" scenarios. They can be toxic or they can help further their careers. Men and women form close relationships all the time at work but nobody seems to care too much about those because there is no sexual inuendo around them.

In my mind, a work wife/husband is someone of the opposite sex that you gossip, strategize, cooperate to get ahead in the office. Sometimes it's public, many times it's behind everyone's back. Sometimes it's peer to peer, other times it's a leader/follower scenario (man boss, woman admin). But generally this is done without spousal consent and sometimes goes sexual.

One of my bosses was taken out and fired by management after a work wife spilled the beans on their relationship after she got screwed over when he got a promotion after being a power couple at work for many years. They were both married to someone else. If they weren't having sex, it would've been a very strange relationship.