Is this guy interested in me or not?

It all started a few months ago when I started a new job. My coworker used to be quite flirty with me, always looking at me and telling stuff like I'm pretty and very good at my job. I didn't think anything about it because he is very talkative guy and likes to joke around. However as the time passed I was fool enough to develop a crush on him....only to find out that he has a girlfriend and they have been together for several years (he doesn't know that I found out that). I got annoyed and decided to be cold towards him. He seemed to wonder what happened and tried even harder to get my attention and when that didn't work he went very serious and barely spoke to me anymore. After one day he immediately sent me a friend request on facebook and I accepted. According to his profile he was in a relationship as I had found out...but the next day he hided his relationship status from facebook. Then he was again nice towards me...and one day I decided to test him a little bit. He said jokingly that it was nice to see me after a long time (we had worked together the day before) so I asked if he had missed me...and he went totally quiet. We were quiet a long time, he only started to talk to me later on some work related stuff...And now things are really awkward, he doesn't speak to me much, but he is looking at me a lot.....Any ideas what is going on? Is he really interested or have I just imagined the whole thing? Just to say I'm not actually interested in getting involved with a taken man, I just don't have any idea how to act around him because we are coworkers........
Is this guy interested in me or not?
Add Opinion