Hi there
I can see that you are struggling a little to manage this friendship, but this is something that you can work on. If you are willing to look at what's happening inside you can learn a lot about yourself.
It seems that you need a bit more from your friend that she is either not able, or willing to give. She likes to have lots of friends but you enjoy the intensity of one, best friend relationship. It might just be the case that you have to accept that you are both different.
A healthy relationship between two people, means that you will always be accepting of who the other person is and makes no attempt to change them. When you try and change or control someone it can often have the opposite effect and can lose the friendship. When you think about it, why would you want to change the very qualities that probably attracted her to you as a friend in the first place? Feelings of jealously can leave you feeling threatened, when your friend is hanging out with other people they are not replacing you, but they are just other friends.
Try and just accept that you feel a little jealous, and then when you are with her enjoy the time you spend together, and what about you also finding some different friends. You obviously have the qualities that attract friends or else this girl wouldn't be your best friend, so what about finding a new interest and making some completely new friends that you can hang out with?
Check out the Friends message board and see what other young people say about friendship. You can also always contact a ChildLine counsellor by email, calling 0800 1111 for free or in an online 1-2-1 chat.
Take care
Sam