Should I be mad?..........................…

Well there is this boy who I really like and I went out with him for 3 days until he dumped me. Now he is going out with my other friend, lets just say her name is Martha. There was just a school dance and they danced together and then they kissed twice and they have only been dating for 2 weeks. I cried when I got home after the dance. Should i be mad at her, because when me and that boy were dating she was so mad and now she is dating him. Please help me!!! :)