I think one of the most frustrating times of my life was when I developed a crush on someone I couldn't have. It was so intense it was physically painful when we were apart. The obstacles were not quite the same as yours--we were each attached to someone else at the time. Nevertheless, I know what you're going through.
There is no easy answer. Most people will tell you, as was told me, that the only way to get over him is to not see him and move on. That's easier said than done because the attraction is very intense, AND this is your job. How easy (or realistic) is it for you to pick up and move to another job?
Another obstacle is that he's married, which implies (unless you know differently) that he's straight. Even if he swings both ways, he's still attached and cannot devote full attention to you. Lastly, he's your boss and even if the other two obstacles were overcome, the last one could get messy and complicated in a boss-subordinate relationship--even if he was agreeable to it.
I, too, thought that merely hanging out with him would be enough--just to interact and be physically present. But, it really wasn't. I wanted more and just hanging out was soon not good enough.
So...what to do? I would recommend finding a good therapist to work through your feelings on this, and what your options are. That's what I did. It helped to talk about it, but the advice (cut off all contact) wasn't realistic and seemed to be even more painful. I think you need to keep talking about it to a professional, and to explore what realistic options you have and how you can move on. You're certainly not alone in this.
In my particular case, over a period of 3-4 years, both of our circumstances changed, we became available, and hooked up. We've been partners for 18 years now and it all worked out. I never gave up on my dream with him and to be really honest with you, I'm not sure I could have. Had fate not been the way it was, I would have had to figure it out and get over it. I think time would have been my best friend in having that happen. But, it would not have been easy.
Good luck with this. I know it hurts and is frustrating as hell. It's really tough to figure this out on your own, and it really does help to find someone to talk it all out with. They aren't involved, and thus can help you put things in perspective and help you deal with your feelings and channel them in good directions. Let us know how you're doing and what happens.