Zatanna and Bruce have hooked up in the past, but Zatanna is still more than just a love interest in this context, considering that they're childhood friends in the current continuity and she's one of the few people with the full picture of his life story. She thus falls into this very small category of people who:>knew him before he was Batman>knows his secret identity >met him through other means that is not superhero-work related>is a peer in a similar age range rather than a mentor>not likely to put up with Bruce's bullshit because of aforementioned points
These elements tend to create interactions that hit different from his interactions with Alfred(father figure), Clark and Diana(colleague), Selina(love interest), or his kids(duh).
John fulfills all conditions save for the first one afaik. Unless they met during Fortunate Son or some shit, idk, I don't remember what happened in that story.