They're simply office mates who also happen to be soul mates.
Or, to use a term that has come into vogue, Ms. Hiddema and Mr. Ducoffe are office spouses corporate couples bound by mutual respect, common interests and that particular chemistry of friendship
Marjo Johne, "Wedded work bliss: the office spouse," The Globe and Mail, April 5, 2006
As more women find themselves on equal footing with their male counterparts, a new workplace phenomenon is emerging: the office spouse.
A recent study by Vault.com found that 32 percent of office workers have an "office husband" or "office wife" that is, a nonromantic relationship and many have more than one.
Ieva M. Augstums, "Do you take this co-worker...," The Dallas Morning News, March 12, 2006
See, those sweet, soothing words were for Sue, the Other Woman in my husband's life. ... Then I remember Sue is his workmate, his pal. He's with the woman I am now comfortable describing as Keith's "office spouse."
Carla Merolla, "Everything but sex: the office-wife thing," Cosmopolitan, August 1, 1996