I was at a small party with some friends, and my friend's sister started sitting in my lap, holding my hand, and just all around flirted with me. My friend left early, because his other friend got sick, and she wanted to go home. (He was there for the majority of the flirting, and he didn't say anything, although he was taking care of his friend who got sick.) His sister stayed, because I was supposed to drive her, and their cousin back home. Her cousin had a bag of weed with him, so I refused to drive him home with that (those are my rules) so I drove my friend's sister. It was really awkward, because she kept staring at me, and giving me weird compliments like "Your so accurate" (Whatever that means) Then after I drop her off, and get back to my house, she calls and wants me to come over. I decline. The next day I tell my friend the whole story, and how weird it was. He noticed how much she was flirting with me, and apparently so did everyone else, because they asked if we were dating. I think he might have told her I thought it was weird, because shortly after, she calls me and apologizes for sitting in my lap, and flirting. I told her It was awkward. She said she was ok with the flirting, but wanted to apologize in case I didn't like it. I told her that she's my friend's sister, and that's weird for me. She apologized again. Then asked what I'm doing today. I told her I was doing homework. She then invited me to watch a movie with her and her brother later, and how she's going to do a fire pit tonight. I decline, and we get off the phone.

I am 21, My friend is 20, and she is 26 (with 2 kids)

What I'm worried about is next week. They are moving to the other side of town in a few weeks, so this next weekend they're having a party BBQ at their house. I don't want it to be awkward around my friend and his sister. Also some of my friend's female friends are cute, and knowing his sister likes me, she might get all hurt if I start talking with a girl in front of her. Then I'm helping them move the weekend after that! Weird situation!