There are some friends who don't mind hanging out as long as you'll come to them every time. Or if your friend only wants to hang out when they need a company for their own pleasure or work. You might notice that your friend is constantly turning down invitations to hang out when you want and then only reaches out when they happen to borrow your car or borrow your makeup stuff. The friendship is probably pretty one-sided and your friend may not value you as much as you deserve.
If you have a friend who constantly talks about themselves listening to your friend talk about their problems, offering them advice, and consoling them, but never get the same effort in return, it's a sign your friend doesn't have your best interests at heart, or they're just really self-centered. Both are signs they might not be the best friend.
If you are friends with someone with whom you are an open book and find yourself always ending up sharing everything about you even your deepest darkest secrets but she never behaves in the same manner, acts secretive then she may not be considering you a close enough friend to trust you. Of course some people are not as expressive and find it harder to open up than others, but if your life is an open book and their life is kept under lock and key, then things are seriously one-sided and that's not what true friendships are about.
It's sometimes understandable to slip up and accidentally reveal a secret every once or twice when you and your friend have common friends , but if your friend is constantly apologizing for "accidentally" revealing a secret that you asked them to keep between you, they're probably not the most trustworthy friend. Either they like gossiping or they just have a blabbermouth and your secrets probably aren't safe with them.
If your friend is constantly insulting you or making fun of you about how you dress up or look or always cutting you off in the middle of your talk in front of other people without being considerate about your feelings. Or if she feels embarrassed with the way you laugh or eat or behave around her. If your friend can't accept your true self then it's a sign she isn't your true friend. You don't need that negativity in your life. Friends should lift you up and make you feel better, not put you down and make you feel small. In fact True friends will love you for you and never be ashamed for people to know you're her best friend.
People who are your well wishes or close to you will always be happy about your success or just seeing you doing well, especially best friends! So if you feel like your friend never has anything nice to say when you achieve something, or instead of congratulating you she starts talking about her achievements and comparing those to you then its definitely a clear sign that she sees you as competition and not a friend. True friendship shouldn't feel like a constant competition. Leave her and move on!