When it comes to friends, we all have our own differing opinions on what it means to be friends. Some think it's a loose relationship where you only hangout during school or work, etc... There are friends you had when you were younger that you grew away from. There are even friends you only know through over people and when that relationship dissolves, your relationship to the mutual friend also dissolves.
Lastly, and most importantly, there are those friends for whom you'd die for. You know the ones; you're in sync with one another but you may have different opinions. You might not even agree on a majority of things, but you still feel a gravitation towards them. These friends are special. They're the best.
My personal philosophy, when it comes to people, is to try to accept everyone for who they are in the moment. I'm unable to dislike someone based on what they will\could be. I can't simply write people off because I may not see myself having fun with them five years from now. Sure, this brings about a lot of hurt when they have to leave or we grow apart. But, loving people in the moment and accepting them on a simply loving level; that is what I try to do.