My world is coming to an end. Please help me, PLEASE.?

There is this girl whom I lived with for 6 months early last year and we were dating for 8. I loved her to pieces, I lost my virginity to her and she has always been in my heart. We broke up late last year, she moved out and I had with several other girls in a period of a few months. Now looking back I realised I still have so much love for her still. She told me she would never have with anyone else but me ever because she still loved me to peices. Tonight she told me she had a one night stand with someone the other night and I was crushed. The only thing I can think of is a noose with my name on it. I know it may seem selfish to feel angry and heartbroken over this but I cant shake the feeling. I cant stop thinking about what she did with that guy. I seriously want to kill him. Does anyone have any advice for me of what I can do to feel better about the situation. (please dont explain how to tie a noose and PLEASE dont tell me to eat chocolate or ice-cream). Im a 17 year old male. Help me.