My husband is my closest best friend. I know lots of women and probably one of those closest to me is a long-term client of mine - we've been working together (virtually but occasionally face-to-face) for over 11 years. Only in the past 12 months has she shared things with me I never knew about her, and I've done the same. but there are still things we see very differently - my beliefs for example, although she asks lots of questions now which she never did before. Perhaps that's a sign of feeling comfortable with me
I've always been pretty much a loner and haven't had any close female friends since I left high school - that was a long time ago!