I'm not my best friend's best friend, help?

Don't worry about numbers or trying to "fit in". Just be yourself and whoever your true best friend is will be right there with you. Have a talk with Jessica and let her know how you feel- that's what friends are for, to have someone you can talk about anything with. In the meantime, try branching out away from the clique and meet new people. I'm sure there's other girls nearby that you never even noticed who are feeling the exact same way. It's always good to have "back up buddies" and who knows- they may just become the best friend you don't have to compete for. :)