Well... being that we are all imperfect humans, we can't expect for people to always be there. Life will teach us that sometimes that even our closest friends will do something to hurt us. But just because that friend acted that way, doesn't mean they are not your friends, I mean... unless they keep hurting someone over and over and over, we don't really need them in our lives.
We ALL have our faults and the best thing we can do is try to look at the good in people as much as we can, forgive each other and be there for each other. This goes both ways, it's not just a one sided deal. So both of you have to give and receive. When you find a person like that... you can say you have found a good friend in your life.
Take a look at some of the friendship examples in film... like Anne of Green Gables. Anne & Diana were bosom friends, but they even had their ups and downs, but in the end, remained true friends.
In the bible... we have Peter & Jesus. Peter denied even knowing Jesus but after Jesus resurrected, he forgave Peter and left him big responsibilities even. He wouldn't have done so, had he not considered him a great friend.