Search Results: older girls with younger guys

So, I started dating this guy a few months ago and he’s amazing. The only thing I don’t like about him is his relationship with his youngest sister. For reference, he’s 18 and she’s 15. I really liked his sisters at first and then his youngest sister started acting a little weird. Every other time we hang out at his house and we’re in his room, she barges in and starts talking to him and doesn’t acknowledge me unless I speak. We get along fine but I think she’s just a little shy. Recently, his youngest sister has been all over my boyfriend. I’m not talking about hugs, she’s constantly touching him, whining to him about things, I’ve seen them wrestle a few times, every time they stand/sit near each other she constantly touches him. Whether her foot is on him somewhere or she’s holding his arm or shirt or touching his abdomen. She also talks to him about inappropriate things, and when they sit next to each other she props her legs up on him. And on one occasion I saw him smack her butt. And twice he’s told me that he fell asleep in his sister’s bed (both of his sisters share a bed). And she’s made weird inappropriate jokes to him before. Once, she was on all fours looking out his bedroom window and she said “help *his name* I’m stuck”, with a weird tone, when she clearly wasn’t and got up after a few seconds of him not responding to her. I wish I didn’t feel so weird about their relationship because it feels odd to feel that way. But I can’t help how I’m feeling. I’ve tried to ignore it but I just get a really weird vibe and it makes me super uncomfortable. Also she reads smut so I know her mind isn’t pure lol. Before someone questions that.

*Also, for reference, all I have is an older sister. So I don’t know if that behavior is odd or not and I’m trying to figure it out*

So what do you guys think? Is it weird or am I just being insecure? I want to talk to him about it I just don’t want to put him in an uncomfortable position if this situation isn’t actually weird.