ok so this might be a little different than what i was thinking at first but i just got an idea. maybe they could have felt some chemistry initially and gave it a shot, but their nightmare schedules just made it really hard to actually get together and pursue anything romantic at the time. they could have kept in touch as a friends and now they've got a flirty friendship going on? we could play around with it and see if there's something deeper to it, like one or both of them sorting through the remains of whatever they were trying to make happen when they first met, or it could just boil down to them being really complimentary and affectionate with each other. if that's not really him though we can always say they ended up dating around that time and with the both of them being so busy, it just kind of fizzled out.