He's an alpha kind of guy and very independent, so this is a good profession for him. And you're a book store manager. Occasionally, one of my bookstore customers does find out that I am an author, in spite of the fact that my staff is expressly forbidden to tell anyone. I'm most comfortable with anonymity. Too much attention makes me feel inhibited.
Writing seems to be such an independent exercise.
First, your imagination produces this idea, either a plot or some characters in search of a plot. And your collaborator's imagination also produces an idea, a different idea. Lacing the fragments of two imaginations together into one story is complex. It's so true writing is an organic process. Even shifting the setting of a scene can profoundly affect the story.