I have shared an office and a train home five days a week for 20 years with a chap I’ll call T. He calls me his “work wife”.
He does have a real wife and family. I’m many years divorced. Our relationship is very sibling-ish, and we’ve become, over the years, very close – we share things we don’t share with our “real” friends and family and just by virtue of the time spent together, we have shared a lot of our lives. We have never socialised outside work, aside from at work functions, and have never been to each other’s homes.