I spend much more time interacting with my work spouse than with any other co-worker. We trust each other with things we wouldn't necessarily take to other work friends, like plans for our careers. We also provide for each other: snacks, Tylenol, contact solution, a fresh pen, whatever.
Personally, I have seen the pattern quite often, but never saw a name for it until today. A "foodies group" kind of relationship, that happens to be strengthened by things that might have lead to something romantic had they met in a different context. Even the name chosen hints at it not being an overly romantic state: it skips right over date, girlfriend/boyfriend, bride/groom to the wife/husband stage which can be more like a well worn in mechanism than like an uncontrolled infatuation in many cases. It (jokingly) references marriage as in "old couple", not as in "a pact to raise children".