I've never had a constant 'best friend'.
There isn't a single person that I grew up with that I talk to regularly, let alone hang out with them. Given, I've never been one to attach myself to people because the friends that I would make would either cause drama, or one of us would move to a different city.
Despite never having a regular sense of a best friend, I've always had my family. I've known my family for nearly two decades, and that's the longest I've ever known anybody. And because I'm the baby of the family, they've known me longer than I've known myself.
Because of how close my family is, I can honestly say they're my best friends.
They always have your back.
If anyone is mean to me or makes me upset, I GUARANTEE you, my older sister will find them and make them wish they were never born. It's happened. Multiple times. She isn't afraid to make enemies on my behalf. When I was in elementary school, I was walking home from the bus stop with my brother a few feet behind me, and this kid that got off at our stop started yelling at me and calling me names. My brother yelled at him and told him to leave me alone, and when the kid didn't, my brother pushed this kid into a sticker bush. And when the kid went to get up again, my brother shoved him down again and warned the kid to stay down until we were gone.
They're proud of your accomplishments.
My dad went to every single one of my drama performances. Two weekends, eight different shows. Every time I was in a play he went to all of those performances, just for that particular play. And when my older sisters couldn't make it to the performances, they sent me flowers. At any graduation, award ceremony, anything, when my name was called, my family was the loudest out of anybody. They knew how hard I worked for whatever it was that I achieved, and they would let me know just how proud they were.
You can be weird with them.
And bonus: they'll be weird back. Half the time we talk about weird things, and the other half we spend making strange noises at each other. We make elephant trumpets at one another, screech for no apparent reason, and call out for each other in weird voices, because well, we can.
They'll help you out.
Whether it's money, a place to stay, or you just need physical assistance, they'll help. I've dragged my older brother along to more things than I can count. I woke him up at five in the morning to road trip with me four hours to the Canadian border to meet a character from my favorite tv show, just so I could use the carpool lane through traffic. This is the same brother that when I was in a musical my sophomore year, his senior year, I forced him to work as a member of the crew because we were short on staff. He's not happy about it, but he does it anyway because he has to.
They get you like nobody else.
It's never difficult to shop for each other because you know them. For my oldest sister's birthday, I know to stalk her Pinterest, see what books she's interested in, and buy her the whole series. My other sister, I know to stock up on apples and peanut butter when she comes over. I know my brother well enough to not ask him what he wants for dinner because the answer is always pizza. If I find a stupid play-on-words joke on Facebook, I tag my dad in it. And for mothers day, we always get my mom some sort of cream that smells like lavender. We get each other.
They love you...
No matter what. You can never stay mad at each other for too long because at the end of the day you know you love them.