I then suggest asking your boyfriend how he would feel if you were texting and on FB with his best friend all the time.
As for your "best friend", yeah, no she's not. She's being sneaky, she's lying and thus disrespecting your friendship. If you want to say something to her then tell her you already know what she's been doing, you don't appreciate it (I mean, it's just bad form.) and you'd like to know how she'd feel if you were texting her BF (if she had one) all the time.
Sometimes the only way to get people to understand their douchebaggery is to hold up a mirror to them. Figuratively speaking, of course.