There is nothing wrong with you and it isn't your fault. You really haven't found the one yet, but there are billions of people on this planet, so don't give up hope.
High school especially can be a brutal place. So many things change over time and lead us down different paths that we never saw our selves venturing down. Sometimes it's with people we've known our whole lives, and sometimes it's with people we've known for two months but it feels like forever. You never know just who you're going to meet and what kind of impact someone can have on your life, good or bad, but these impacts will always leave you a changed person.
I was always jealous of people who could say they've been friends with someone since their childhood or post pictures on Instagram of their thirteen year friendship anniversary. The longest friendship I've ever had so far has been barely six years. I never had a connection with someone on that really deep level that I could just be with forever, and that's okay. It's natural for people to grow up and grow apart. If you're not losing friends, you're not growing. I always thought I was a bad friend or I was doing something wrong because my friendships didn't seem to last as long as everyone else's, I never had that lifelong friend, things just didn't go that way for me.
Looking back now, I'm glad that those people are no longer in my life. I can obviously see that it just wasn't meant to be and I was headed down a different path that I certainly didn't see myself on. But here I am, stronger than ever. I know the qualities I want in a friend and the kind of people I want to surround myself with. I know how I want to be treated and how I want to treat others because of my bad friendships. They taught me a lot about being the friend I've always wanted for myself.
If you never have had that "best friend", don't give up hope. One day you will find someone that makes you understand why no one else was good enough. There is nothing wrong with you, you are just trying to figure yourself out. Life can take unexpected turns sometimes and we become friends with the people we least expected, and sometimes we lose people we thought we couldn't live without, but life will always go on. There's nothing wrong with not having that best friend yet. You should never settle for anyone that's anything less than what you deserve and want in a best friend.