Reject her.
Most likely he found a girl that he likes and doesn't wont to make her jealous by having a girl as a friend. That or you did something that he didn't like.
I suggest that you talk to them and tell them why they are saying that someone else is there best friend that's my advice
The rebound, i suppose
If you still like your best friend then try to get her back or let her go with your sister if that's what your friend wants. Or mabey your friend could be friends with your sister and best friends with you.
If you like it, kiss him back. If you don't, break away and tell him, "No!"
If your best friend is honest and caring and looks out for you then he/she would be your best friend but if they're mean and say nasty things behind your back then they are your enemie
Your best would come back because he still values you. And it is for that reason he has best attached to it.
If your friend decides to stop talking to you, it is usually just a phase, and after some time, she'll come back to you, if you really are best friends. If her new 'best friend' is changing or having an influence on your real best friend, you should try to step in, saying that this is wrong. If you're worried, the best option is always to just talk to her. As the phrase goes, 'If you love something, let it go- and if it comes back, it was always meant to be. If it doesn't, fate had other plans.'
just tell your best friend that you really like him and see what she says about it.
It means that he wants to become your best friend. There's nothing wrong with him bring your friend unless you have a problem with it.
show her that you can make friends without her.