How to tell your best friend you don't want to be there best friend anymore?

well we been best friends for 9years and im alway been more mature then her and well she's really DUMB im not kidding like really & i feel bad cause she dosnt know that she is & its like she wants nothing in her life all she talks about are dumb boys and how they cheat on her and stuff or how she saying she over him shes very stupid im sorry for calling her that she had & i belive she had gotton an std she wouldnt even tell her mom and she says stupid **** like i juust got baptized & i told her & she goes well i dont know why your still going to act the same i was like thanks that was nice to say and not that im baptized now i see stuff she dosent & its not holding my back or anything how do i say grow up or do somthing ! ya know i feel bad and i think she know we GREW APART but i would love for her to be there always i just want her to have a brain! shes not were i am & im not were she is i dont want to be friend anymore but i want to be there for her.but not in a dum shell