It’s called a ‘work spouse’, and yes I had one for several years. We were both single but didn’t really go on dates together, thought it would be a bad idea since we worked so closely together. We did go to extra-work functions together, and out with friends as a group. No hanky or panky, but the idea was not far from the surface. The corporation eliminated her position, but waited until I was away on vacation to do so.
A few years after that I married a woman who is part of a large, extended group of friends which includes my former co-worker, also now married. One summer we were sitting around a campfire with a large group of friends, including our spouses, and she described us as having been ‘work spouses’. That was the first time I heard the term.