I've been going out with this guy for almost 6 months now, and I really like him more than any of my ex boyfriends and not just because they are my ex's, his parent and his siblings like me and my friends know him too. We all go to the same school and for some reason she always try to sit between us. She calls him her brother and she claims that it's because I'm her play sister, not to metion she's now dating one of his friends.

Should I be worried that she might have a crush on my boyfriend?

Probably... in my experience girls are very.. scandalous and two faced towards each other in most cases, she sees how happy he makes you.. and they start thinking "why can't i have that?"... you won't get a straight answer... just trust your guy to tell you if she makes somewhat weird advances towards him.. if it comes to something going down.. they secretly have something going on.

I disagree. I think she is jealous of you, and is afraid of losing you.
A best friend is far more important than all the boyfriends you will have, so treat her gently. Tell her she isn't going to lose you, give her a big hug, and say she doesn't have to worry, and at some time just say hey, I want to sit next to my boyfriend, you sit on the other side.

Even if she does have a crush on your boyfriend it shouldn't both you. You are the one dating him, and if he really likes you and you really like him then there shouldn't be a problem.agreed, but you can't put it past any female these days, my points on women these days are legit, she should at least be cautious.

What does your boyfriend do or say when she sits next to him?

Next time she tries to sit between you, snuggle in closer to your boyfriend and offer her the seat beside you, putting you in the middle.

If you're not telling her to stop, you can't expect her to.

She is rude, and between the both of you you have to set boundaries. Start by telling her sitting between you and your boyfriend bothers you.