am I over protective?

so I recently told my semi friend about my boyfriend and the first thing she does is DM him on social media and starts trying to flirt with him. I am 100% fine with him talking to girls but I'm not fine with him talking to her because she has always tried to take away my bf and/or crush at the time. but I don't want to tell him that he can't talk to her because I don't think it's my decision for who he can and cannot talk to, but she is a fucking skank. I just don't know what to do because I'm just wondering what they talk about