The life and friends are two connected things. As life is one we get friends for once too. There could be so many things between friends sometime we get angry on. But If you don't solve and remain angry then that will be your big mistake and it could be just because of your ego. One side can take step to solve it but your ego (that is not fully ego but a kind of ego for that you think you were right at that moment and another one should take step first to feel apologize) never let you to do so. You should be apologize to be a good friend. Now you may think why to apologize if another one doesn't care at all. Then whats the difference between you and that one. You may leave it by thinking you dont need or you may proceed to solve it. It shouldn't be difficult to apologize with friends.