Maybe you would be willing to share the age difference between you and your sister. I’m going to assume it’s about a year or two, since that’s the toughest age difference. Your sister wants her own life and to hang out with her own friends without having you hanging around all the time. She is probably mean to you deliberately, because she can’t divorce you or something like that.
It’s probably lonely, especially if you’ve done a lot of stuff with her over the years and you’ve been good friends. But now she wants to do stuff she doesn’t want you to see.
There’s not much you can do to get her to like you better. She does like you. That’s not the problem. The problem is that she wants her own life, and that means she can’t have you around. So to you, it feels like she doesn’t like you.
All I can say is to be patient. Eventually you’ll grow older and she’ll feel like she can share her older sister stuff with you again. Maybe she has a boyfriend. Maybe she is doing other things she doesn’t want you to tell your parents about.
Your best bet is to make your own friends now. You have to give up your sister for a while. It’s not permanent. Just a few years. Make your own friends and be independent, and before you know it, she’ll be coming back to you.