It amazes me how many people complain about a friend pulling away from them (or just breaking up with them altogether) after they admit that they did do something negative (yell at them, go off on them on Facebook, spill their secrets, talk smack about them behind their backs) to their friends. It's as if they don't realize that their actions have consequences.
Now, I get that we all have bad moments. No one is immune from behaving like a schmuck occasionally. But when you behave badly, your friend is not required to forgive you, especially if you did something particularly hurtful. Typically, friends do forgive each other and move on, but only if there is responsibility taken and apologizes made.
If you do something hurtful to a friendship and you don't apologize, your friend may still forgive you. If you think you're getting away with something by not apologizing, however, you're wrong. That second chance your friend gives you may just be your last, so if you don't cherish it and do the same rotten things all over again going forward, your friendship might be done for good.
Your friend might also forgive you but choose to stay away from you. Everyone has busy lives where we need all the positive support we can muster. So if someone is treating us badly, we might pull away because honestly, who needs that type of negativity in his or her life?
All of this is to say that if you mess up, take responsibility. Care about your friendships enough to be an adult and say you're sorry and do better. If a friendship ends because of your own carelessness, it can be a hard thing to accept.