A person at work you go to as your favorite person to talk to, eat with, perhaps exercise with, hang out, or even talk dirty through texts or IM's
Friend: Dude is that chick your girlfriend?
Me: Na, it's just my work spouse.
A significant other you work with, whom you connect, share, and spend time with exclusively and intimately in the workplace. Both parties are mere aquaintances outside of the workplace and are completely unknown to each others true and respective domestic spouses.
"Rumor has it that those two are dating."
"That's completely untrue. Heidi is just Allan's work spouse. That relationship ceases to exist after their 8 hour shift."