Do I make a move on this girl or move on?

So, my situation’s a little weird, and now I find myself here. When I asked this girl out, I actually had no idea she was dating somebody…, and that somebody I happen to work with.
I mean, I looked at Facebook, says she’s single, no pictures of other guy whatsoever. I asked her to hang out out, she obliged, and after a drink or two, she was all over me. At this point, I don’t know about said guy, but from our conversations tried to walk cautiously..I actually don’t like stealing women away. I mentioned I was going salsa dancing…and SHE ASKED ME if she could come. And she did, and we had fun, but by now it was pretty clear what was going on. She does seem unhappy with the guy, I” say that. Now, this is where it gets uncomfortable. The following week, she invites a bunch of people out salsa dancing…including her boyfriend, which is now plainly obvious…except…who does she dance with? Me, for the majority of the night, and who does she grab by the shoulder and flirt with? Me. So now, I feel like a douche, and I really don’t know which way to go at this point. My first thought is, “she’s just trying to make her man jealous, so they can have a heated argument later,” is about the only logical thing I can come up with here.