It's really tough to act like nothing happened when someone has really hurt you--and often times, its not a good idea either. When I've been truly hurt in the past, I will usually draw back for a while, and think about what happened between me and the other party. I'll try to understand their actions, and the whole situation. Most of the time, I can usually come to some understanding as to why they chose those actions, even if they wouldn't have been the actions I've taken. If I really don't understand, I might go to them after a week or so and ask them to explain why they did what they did.
Then I try to decide if those actions reflect the kind of person I want to associate with. If the answer is yes, I'll go talk to them, and try to make peace with what happened. If the answer is no, I will go my separate way, because I know no one is benefiting from the friendship/relationship.