Most Helpful Guy
First, I'm sorry you are hurting, asker. One way or another, try and remember "and this too shall pass."
Now, no one can say why he decided to not pursue a relationship with you. Certainly I can't. Will he come back to you? Well, I can't answer that either. Possibly. I think perhaps you should set limits on to how long you will wait for that to happen.
If he doesn't come back to you, then I'm afraid time is the greatest remedy. That and staying active. It might be useful to take some time to reflect on what you've learned. Perhaps there's a lesson here about dating someone you work with. Understand that no matter how much we may want them to, most relationships don't work out. I'm not saying love is a fairy tale, it's just statistically most relationships end with pain, some sooner than others. Given that this is the case, perhaps it's best to steer clear of men that you work with as potential romantic partners.
Here's one way you can get your hopes up, even if he doesn't come back to you. It would appear that he was attracted to you on some level. If you attracted him, you could attract others, too! In a world of 3.5 billion men, I don't think there's just one man for you, but many. If you attracted this guy who left you, then you can attract another man. A man who will love you back the way you love him.
I often felt the same way that you feel right now when I was 22. You've attracted a man who you liked. That's a good sign, isn't it? It just didn't work out. So you'll just have to attract another. Remember, if not him, then someone else.
You take care now.