Is my sister sexually abusive towards me?

Have you ever felt like someone you have known for years someone closest to has been sexually abusive? Well for me that's a yes and my younger sister Mia and I have been close to each other ever since we were little we were like best friends. She didn't have friends or a boyfriend she didn't talk about boys either I didn't want to press her about it I thought if she didn't she wouldn't feel comfortable telling me. Early into our high-school years, things started getting weird for example my underwear disappeared and I found it in her room she made up an excuse saying she needed better-fitted underwear but she at least could have asked right? It got even weirder she would grope my boobs I thought it was a joke but she did it more than twice I started to feel uncomfortable and told her to stop she wouldn't she would just say "But they're so big" It always creeped me out when she did that. once she came into my room when I was sleeping last at night and reach into my pajama pants down towards my vagina I had been awoken by her touch but I couldn't risk being caught it would be awkward. I posted it, did I get ya? I was writing all the time you know online help can't be too bad, Julies! My sister called I tensed for some reason at her voice yes I replied she came into my room something just felt off today but I couldn't quite put my finger on it. My sister sat beside me on my bed stroking my hair affectionately I could have sworn her pupils were dilated I was wondering if we could sleep together like the old times she said I replied by saying why all of a sudden she was silent for quite a long while and then gave me a very menacing smile.