What do you think about you or your husband having close friends of the opposite sex?

I have a boy bestfriend since highschool, my husband has a girl best friend since time unknown. We just have boundaries. Kapag may bagong girl sa fb messenger or sa text (pakielamerang wife ako sorry haha), i check if it's just a friendly chit chat or getting flirtatious na. There's a fine line between being friendly and malandi.