I missed my ex and do not know what to do!

Just one year ago, I became friend with a girl who also was (and is) my colleague. The first 3 months went very well. she really loved me and everything was going well. Our conversations on the phone sometimes were more than 2 or 3 hours. To be honest before that relationship I did not have any long term relationship with any girl and those days seemed fascinating to me. After a while everything changed. She started to blame me. On those days some of my behaviours seemed to bother her and after 6 months we broke up. I did not wanted it and even I cried in front of her (it was the first time that I was crying in front of someone). Now after one year I think that I have not moved on and I can not think about anyone else. I am not able to make a new relationship and memories of those days are always in my mind and are killing me. What should I do? Everyday I wish to be my last day of life and even I got some physical disease because of that (like nervous backaches). What should I do know? The worst part is that I still see her in our company and it is ruining me. Changing my job is not possible. After that nothing makes me happy, going out with another girl, being with friends, traveling ... .