What a wise and thoughtful girl. You are asking good questions and looking for help before things get so out of control that you end up damaging relationships that mean much to you.
Here’s what I think I know: Twins are vulnerable to having an especially hard time during the teen years. This is a time when people start to assert their own individuality and begin to separate from their family. It’s a time to figure out who you are as an individual person and to test out your likes and dislikes, to discover your strengths and talents, and to make attachments to peers. When one twin is ahead of the other in these life tasks, the other twin can feel confused, abandoned, and even betrayed. It hurts. It hurts when the person who knows you best, who has the deepest and strongest relationship with you, starts to make it clear that she is her own person with her own life. You are fighting to keep her close. She is fighting to put some healthy distance between you. Neither of you wants to hurt the other, so you stop the fight but you don’t resolve the issues. You aren’t causing the problem. The situation is.
What you really need to do is develop your own friendships and interests. I don’t know why you don’t talk to your friends. It may be that you are so used to always having your twin available that you haven’t given the time and energy to friends that relationships require. It may be that you are changing and you need to change your group as well. Get busy outside of home. Join an organization or team or club and start doing things that matter to you. Try out different things until you find something you truly enjoy. Experiment with ways of dressing that express who you are. Doing these things will help you find people who share your enthusiasms. In short: Put your energy into discovering yourself instead of fighting with your sister.
You can relax in the knowledge that the twin bond is very strong. But love and connection don’t require sameness to survive. In fact, by developing your differences as well as your similarities, you’ll have more to appreciate in each other.
I wish you well.