then what does bff mean?

my friend (who will stay un-named) always tries to steal my boyfriends, and im sorta used to it. but she went too far this time.
she was texting my boyfriend on my phone, pretending to be me. and while she was pretending to be me, she broke up with my bf (who is the most caring and loving guy in the world :) ) and then called him on her phone and she asked him out. and he said no it was too soon (so sweet huh!) then she just started yelling when i came from the changing rooms (this all happend at the mall). and she hung up with him and i grabbed my phone and i asked her what did these new text messages mean (cuz he was trying to get me back) and she got mad at ME! as if i was the 1 to do all that right! well now im going back out with my bf and my friend said that she wont ever do that again...but should i belive her? i dont have any idea on what i should do : / help me please?!