Kinda worried about my friend being stolen ?

Ok so, my best friend is a guy, im a girl. We've only been friends for a year but we both agree that we're best friends. I know him almost better than he knows himself. He asks me to answer questions about himself sometimes, but that's not the point. So now you know how good of friends we are. Ok so the problem is yesterday during recess (yes we still have recess in 8th grade) I was trying to talk to him, and this girl um let's call her Jill. So I went over to a group of my friends and he was there so I was about to talk to him and Jill pulls me away because she says that we needed to talk. So I go talk to her, then when I go back to the group he leaves and they start to talk. They talk all recess I go and sit down by this tree where we used to talk a lot. Then my really happy preppy friend comes over and talks to me. Then recess was over, so the problem here, which may not seem big, but I've had some trouble lately with Jill. So the problem is two things. I'm afraid that she might try to take him and I know she's bad news. And two she's saying things, and acting like she knows him better than I do which is impossible. This is just really upsetting and I'm not too sure what to do. I've thought this over and I'm not sure. So what do you think? I just really like him as a friend. We might see each other on Sat. at this party. Thank you in advance!