I don't think you are over reacting. No good friend would date a guy you felt that strongly about! Even though she did you wrong, don't be mean to her, but make sure she knows you do not plan to be friends with someone who would do something to hurt you like that. A similar situation happened to me when I was your age, and I stopped talking to my "friend" for a year. After I fell in love (with the guy that is now my husband) I was able to forgive her because I knew that relationship wasn't meant to be, and she ended up marrying my ex! Everything worked out for the best. The pain you feel right now is REAL, but try not to say or do anything that you may regret. You have a right to end the friendship, and it is wrong for her enter a relationship with a boy you care so much about. Hope this helps!