Is it normal that my sister is curious?
With our parents constantly working, and our older brother being a piece of shit, I practically raised my little sister. When I was 18, and she was 12, I moved from Unspecified City in Eastern Canada to Unspecified City in America to pursue an education just before her thirteenth birthday. That upset her, and we rarely spoke, though she'd always come to me when she had a problem (puberty, school, sex, and the likes). So, four years go by and I get a call from my mom, asking if my sister could come live with me. I, of course, agreed. I saw her for the first time in four years, and she's like my younger clone, but with dark hair.
So a few months go by, relatively normal. She knows I'm bisexual and I introduced her to my girlfriend. We've basically been attached at the hip for the past 6 months.
Here's where the problem is. My sister has always been afraid of thunderstorms. Everytime there was a storm, or she had a nightmare, she'd always come sleep in my bed. About two weeks ago, there was a really bad storm, and she comes to my door, asking if she can sleep with me, and I say yes. At about 3:30, I wake up to her hands all over me. I think, okay, maybe she's just having an active dream, but I listened to her breathing and knew she was awake. The stormy weather kept on for two more days, and she keeps sleeping with me, and her groping is getting a lot more personal. Touching me breasts, grinding against me, groping my butt. Twice in the last two weeks she's come to my room at night, saying she had a nightmare.
I don't know what to do about this. My knee jerk reaction has always been to give her what she wants and spoil her. And besides this, there hasn't been a single problem with her. She goes to school, gets straight A's, keeps her room clean, always listens to me, and is even looking for a job. Do I just let her have her fun? Should I talk to her about it? Things have been going well, and I don't want to ruin things by putting her on the spot. Is this a curiosity thing, or is she specifically attracted to me? She hasn't shown any attraction to anyone thus far, besides her fascination with Captain America and Thor.
Any advice would be appreciated.
tl;dr I'm 21, my sister is 16. I'm pretty sure she's sexually attracted to me. What do I do?