Although they were equal partners in running the company and were aligned in what Mr. Black refers to as their core values — “if you lead with kindness,” he said, “you’re not going to kick someone in the shins afterward” — they fell flat romantically. Despite couples therapy and intimate getaways, Ms. Griffin-Black said, “it got to be too much and we realized we couldn’t ‘have it all’ together.” They divorced in 2007.

Here’s where things get interesting. For one thing, the couple’s relationship continued to flourish after they split: As co-chief executives, they continued to spend every day in each other’s presence, doing all of the things that married couples commit to: parenting, splitting finances, meaningfully communicating, confessing, forgiving, even occasionally touching. For another, and here’s the really curious part, EO Products took off in unexpected ways. Whereas the usual story line would suggest that a divorce in such a situation would spell professional disaster — Michael Funk says that in his 40-something years he’s rarely seen it work — EO not only survived the Blacks’ very conscious uncoupling but gathered steam. The line expanded and popped up in retail stores like Walgreens, CVS, Walmart and Target without any compromises made to transparency about its ingredients. “What I admire about EO is their commitment to using essential oils in spite of their being more expensive,” Ms. Quimby of Burt’s Bees said. “They’re willing to go for that level of quality.”

‘We’re a Package Deal at This Point’

As Brad and Susan led me on a walking tour of their offices, which they moved into in 2012 and, later on, their manufacturing facility, their rapport seemed warm and relaxed, both with their employees and each other. Their work space is an open floor plan, painted white, with skylights, windows and plants scattered about. No one has an office except for Mr. Black, Ms. Griffin-Black, and the head of human resources. The couple’s own offices, across the hall from each other, are unprepossessing to the point of minimalism — equipped with a standing desk (for Ms. Griffin-Black) and a stool (for Mr. Black), couches and various personal items, such as travel photos and Buddhist memorabilia.