Hate my bff hanging with others

Please don't judge me for this I already get picked on enough but I don't really like my best friend hanging with other people or going to their house and i don't know why I think it's because I'm afraid she'll like someone more than me or she'll stop being friends with me and leave like everyone else has I don't know what I should do I need advice, please keep your mean comments to yourself...I'm only 13