How one can ruin your life so easily?

I am sure that the problem that i am going to share with you people is not going to be different. Its happening with almost everyone out there. But, i am sharing this with you people because i want some answers from everyone here, i want you to tell me what to do with my life now. I was not the same person that i am now, 6 months ago. A girl, also my classmate to whom i loved so much that i forgot everything in my life when she was with me. Those were the best days in my life. I was happy. I spent my days and nights with her, wandering here and there, laughing, sometimes crying and sometimes quarrelling with each other. I was mad for this girl. Then suddenly, comes a twist in my life. She starts dating her ex again and after almost 2 months of everyday fights, frustration, abuses she told me that she don't love me anymore and i am the biggest mistake of her life. She blocked me from everywhere, from facebook, from gmail. She changed her mobile number. 6 months later.. she is happy with her ex and also she got a good job. And after 6 months, here i am. still sitting in my room, crying for her, missing her, seeing her everyday in my dreams, struggling to pay the rent of my apartment and jobless. She is haunting me in my dreams. i can't eat, i can't sleep, i can't go out. Every girl i see, reminds me of her. People say, its over. Go and enjoy with your friends. But, i can't do that. All my friends are mutual friends. Whenever they start talking about her, it feels like someone is stabbing right in my stomach. I tried hard to keep her out of my life. I tried a number of things to keep her out of mind but all are useless. My final year grades sucks because of her and thats why i am not getting job anywhere. So, all of you who is reading this i want you to comment on this. Every single advice from you is usefull for me. There is no one who can guide me to overcome this. This is my final hope. Please help.

First off, yeah, you had a good couple months with this girl. You had good times and bad, and like relationships many times do, it ended. its not the end of the world. You need to develop yourself. Join some clubs or groups, sports activities, get involved! This will take your mind off of her to an extent. Also, you will find love again. YOU WILL. trust me. Ive been there, done that. You think the world is ending and just when youre about to give up hope, you find someone even better. Hang in there. The point is, if she doesn't want you, is she even worth having? You deserve better. How old are you by the way?

@KALEIGHBEARR90 thank you very much first of all. your advice means a lot to me. I am 25 years old.

@ JJDAILY .. thank you very much. And yes you are absolutely right.. :(