I know this topic is 4 years old and that this argument may very well just be an anime thing (cuz it's based on hearing), but there's something that's always bothered me:
in episode 176 at 16:07, Haibara imagines Gin calling her 'Sherry' a few times. of course, the last one is hella menacing and evil. but the first 2 sound undeniably gentle and soothing. I can only imagine this to be something from Haibara's direct memory of him. that is not a voice you use against just an every day colleague. that is not the voice of a potential rapist and stalker.
that, ladies and gentlemen, is the voice of a guy who bothered to remember a girl's hair, favorite color and favorite flowers.
on the point that Akemi said Shiho had to get a boyfriend: we're talking about the series where it took a rough 900 episodes for the main ship to become an official couple. even if Gin and Sherry weren't officially dating, it doesn't mean there was nothing going on at all.