My best friend is irritating me ?

Ok so i have a best Friend (rosie) who i have been best friends with since we was in nursery and we are in high school now. When we got into high-schooll we grew apart and met new friends. she ended up kinda blanking me out and i didn't like that. juring this summer holidays we hanged out but then it all changed after a couple of weeks, she started hanging out with her friends, one minute she will say i love my bestfriend on her msn and on her bebo she would have " Lara my bestfriend" but then when she hanged out with them instead it was " i love hannah " and i thought whoever she hanged out with she wrote they were her bestfriend. I don't want to hurt her my not been her friend cause i still do i just don't want to hurt her thats all, i need help !!!