Where i work i have a good relationship with many of my collueges some women and when occasionly i have to ring them at weekends or evenings i have a similar level of imformality because i have worked with these people day in day out for years now, the secrecy issue is different, if i was having lunches and social meetings with a woman at work my wife would know about it just as much as she would know if i went to the pub with the blokes from work cos i would tell her, but then my wife comes to my work fairly regularly so she knows most of my close colleagues quite well anyway
It's hard to say wether this relationship would have moved into something more intimate when just reading the situation from the post but it looks like it could have had the potential iykwim
would answer more fully but dd is on my lap demanding i read her books HTH