Based on the responses I’ve received, I’m getting the idea that Risa Aoyanagi and Ryogo Kozuki were not dating and that they were simply partners who had been working together for a long time. I’m always hesitant to trust wiki, especially after I’ve watched the many…creative ways that the Free! fandom butchers it for the sake of shipping.
I’ll be honest - it’s not an important concept to me. I’m far more interested in these two characters as individuals (especially Risa), but I would like to know for sure. For now, I will go with the one bit of factual information we do have - they were partners/co-workers. I suppose I can’t fully dismiss a potential romantic/sexual relationship, but I do feel that she would have reacted more strongly to his death had they been romantically involved.