One of my best friends is jealous & stabbing me in the back?

Okay so at school today my friend alondra is so weird! One of my other friends (Cesar) is a guy and he sometimes flirts with me and I just mess around and laugh. I mean I don't flirt back or anything (He's kinda fat) lol But she has been stabbing me in the back and calling me a slut. I seriously don't know what her problem is & I never did anything to her. And sometimes just because other guys flirt with me she calles me a slut! I mean, how am I a slut im 14 and never even had my first bf yet, I know this because one of my friends told me and i know it's true. I asked her in 6th per. what her prob. was with me and how i am a slut and she said "hmm i wonder why?" she has even told me before that she said behind my back that i was a hoe and she felt bad after. also when im at the feild with the guys playing soccer and sometimes they hug me out of nowhere my good friend told me she'll say "Omg she's such a slut she lets everyone touch her" I mean what is so slutty about a stupid hug!? And she says supposivly i treat her like **** and ignore her but i talk to her everyday and i mean i need some other friends to. and she says im a slut just because i have friends that are guys. it's weird it;s like to her girls & guys have to be seperate she lives in like the old time lol idk what to do should i leave her for my other guy friends or stay with her? becauee she is a good friend sometimes but she is just really getting on my nerves. she'll comment me and say im prettier than her and say "I have nothing" i hate how she is so jealous i wish i could change her