If you really do have a girl that message you talking about them having sex with somebody else, she definitely views you as one of her girl friends, which to most people, can be viewed as a bad thing. Personally, there is absolutely nothing wrong with having a platonic best friend of a different sex. But when you break it down, we guys have been talking to each other about sex and innuendo for our whole lives so it's normal. So when your boy is like "Yo man, I had sex with this girl last night," you're gonna be like "oh snap, forreal, was she fine as hell?" and give me some dap. That's just guys being guys.
But when a girl is like "OMG, I just f***ed this guy last night," you're gonna be like "......uh, why the hell? Cool?" She should keep that kind of s*** to her and her girlfriends. Talking about her latest one night stand and her periods should only be talked about with her girl friends, not her guy friends. I know for me, that s*** is just awkward and breaks the norm.