The reality of the situation is that he is dating someone new. I often struggle with the same type of unrequited love situation that you are in now. In fact just got over one. I think in some situations it is possible to reamin friends, but most times I find that if you had a dating or almost dating type relationship like you are describing it is almost impossible. What you may want to try and do is distance yourself from him as much as possible for a while. It sounds like that will difficult for you since you see him at work, but if you are texting or anything that you may want to try and cut that off. You really don't want to let your self-worth be dependent on one person. I've been there and if they ever finally say they can't be friends its is devastating. Also try your best to meet new people of either sex. And if you have any other friends try talking with them so more as well. Sometimes I get so focused on one person, I forget my other friends are there for me as well. Getting back in touch with them might help you.

I know this is tough. I really wish you the best and hope that you get through it.