HELP? insecure

Hi, my boyfriend and i have been together for 1.8 years. we’re long distance most of the year now because of college. i try really hard not to get jealous or anything of his girl-friends but sometimes i cant help it. there’s this one girl idk y she does but she just gives me weird vibes and upsets me a lot, but they’re friends and i can’t control who he’s friends with and stuff. it’s not even that i’m jealous or think he’ll cheat on me, i think i freak out and overthink because i’m insecure with myself. i’m constantly worrying that he’ll see the same issues i see with myself, even tho he assures me he doesn’t. any advice on how to stop overthinking everything and be more confident?