Friendship is an inexplicable mode of communication which is.. well as i said the wh*le concept is indeed inexplicable what I would from my personal experience point out some of the observed characteristics of some true friendship bonds!
So lets just think about the origin from where these tiny buds bloom from, maybe a shared snack at the canteen, or the first time you get seated with a stranger in a new university or school, or maybe you both have crush on the same guy and in the process of competing in the woo battle you end up realizing the beauty of friendship. For me, most of the friends that i have in my best circle are the people i genuinely disliked initially. HAHAH, some i thought were rude, over-bold (if that's a thing lol) , egoists. But i think the true beauty shines, when you dislike someone, you neglect all their good qualities and focus on elevating the negatives in your head. And after all that negative an*lysis when you finally make that bond, you just know how strong it is going to be!
I had certain people that i used to call friends who would love if i succeeded but hated if i succeeded above them, who hated whenever I got more attention, and manipulated me into believing that if i took a step which could be incredible for me, but would create a negative reputation. I was sensitive, desperate and insecure, till i realised they made me that! So if you are in that circle, you will be heartbroken again and again, so better leave!
You will find people who will always encourage you, they'll warn you what you're doing is wrong but when you hit the rock bottom they will be there saying "I told you so!!" but they will give you a shoulder to cry on!! That is what you deserve!