Margaret Weis and Tracy Hickman (a man) wrote several fantasy best-sellers together. I think they both had spouses and as far as I know, where not an item.
The only possible one that springs to mind are Deborah Kaplan & Harry Elfont, who co-wrote and directed Can’t Hardly Wait and Josie & the Pussycats. Kaplan is married to Breckin Meyer, so the two are clearly not a romatic item at the moment.
On the other hand, I don’t know if the two still work together. Their last produced screenplay was Surviving Christmas which was, judging from the credits on IMDB, significantly rewritten by another team and I’m pretty certain that the film was sitting on the shelf for at least a year before it was released (or escaped).
I don’t have time to search for a cite, but I remember reading an interview with Emily Saliers, in which she says that she and Amy Ray have never been anything more than friends.
The more I think about this, the more it seems that there aren’t all that many male/female creative teams in the first place. I can think of a few singer/songwriter teams, but I’m not sure as to the relationship status of any of them.
Dolly Parton and Porter Wagner weren’t a romantic item, were they?
Pop-Up Video said the same thing, if that counts as a cite.
And how about Enya & Nicky Ryan? They’ve written a lot of songs together, and he’s produced most of her albums, but they’re not romantically connected (in fact, Nicky’s wife Roma writes some of Enya’s lyrics).
Another: Peter Yarrow, Paul Stookey and Mary Travers have performed and written songs together for over four decades, but as far as I know, no one in the trio ever hooked up with anyone else in the trio (they all married other people outside the group).
