It takes time to become a 'best' friend to somebody. A best friend is somebody is always there, watching your back. Somebody who knows tu inside out but loves tu anyway. Somebody that tu can trust with all your secrets. Somebody that tu can sit with in silence without it feeling awkward. Somebody tu can discuss anything with. Somebody who tu would do anything for, and they'd do the same for you. Somebody that tu don't feel self-conscious around. Somebody that wouldn't just stand and watch tu fool about, but registrarse in with you. Somebody that tu can call up casually at any time and ask if they're free to hang out. Somebody that tu can easily say 'I amor you' to, to their face. Somebody that spontaneously hugs tu in public without giving it a segundo count. Somebody who would stay up all night texting tu because tu needed their support at the time.
It annoys me when some people claim 'you've my best friend' after knowing eachother one day. Just because tu automatically get on well with someone doesn't mean they're a best friend. As I said, a best friend should be somebody that is all the above. That's how I feel anyway. It's not a fact, no, it's an opinion. But I feel that 'best friend' is a strong meaning. It's not just anyone.
tu have to get to know them, tu have to have a special bond. tu have to spend time together and accept eachother despite the differences tu will find out. It takes time to form a best friend, but if tu find that this person means so much to you, and tu get to know eachother, you'll find that the level of your friendship will increase. Through my eyes, when tu can put a tick siguiente to all that I stated above, then it's seguro to say they're your best friend.