Why do I get jealous and bitter of gorgeous, beautiful girls?

I’ve always been an average looking girl. The problem is I’ve always been a bigger girl. I mean BIG and TALL. Not a lot of people like me at all and kids do not want to hang out with me in somewhere too scared. Boys in middle school were terrified of me. I was skinny until I got to high school and I gained so much money and I was this HUGE tall girl. I’m 5’11 3/4 and I’ve been that tall since I was 13. The biggest I was is 266lbs. I did lose weight but I still look big. When I see girls that are gorgeous, I can’t help but get jealous but I don’t want to show it. Even guys I like would stare at them and say how hot and gorgeous they are. My best friend is beautiful. She turns heads but I don’t. I’ve always been known as the friend. I get told that they only see me as a friend and nothing more. I’ve never been told I was beautiful by a guy until my ex boyfriend but he dumped me for a petite girl. My dad calls me beautiful but that doesn’t count. My brother doesn’t say it much. He’ll say I look terrific and fantastic which I’ll take too.