I had this happen to me in high school, more than once too, my mom reacted in a similar way, but then would calm down. Poor woman I put her through a lot, still do. Sometimes parents just don't understand how to react when they find out information like that. They feel guilty, or like it is somehow their fault and they react poorly. Give you parents some time to process the information given, then sit down and have a calm but truthful conversation.

As for your friend, I have always chosen to forgive and forget in those situations. Had my friends not gone to my parents or teachers I would not be here right now. Yur friend only did this because they care about you. Have an honest convorsation with them, you can tell them how you are hurt by what they did, but try not to hold a grudge on it!