Why is this b*tch trying to destroy my family? The family she wants!?

Okay, my bf and I have 2 kids together and this b*tch has a son by my bf, but bcuz my bf and I are trying to work on OUR relationship/family to make it better, this monkey azz b*tch is trying to break us up! Sending him letters, calling his homeboys to have them p my bf a message, writting "myspace" blogs about me, calling his mothers house. I'm tired of this crap!! It makes me feel like I am living a lie, bcuz I always wonder if he is really trying to be with her behind my back. But on the other hand, this trifflin snob is tryin to make it seem like that. And I would rather trust HIM over her!! Why do females do that? And what should I do?