How do you keep yourself from crossing THAT line?

I hope you all know which line I'm talking about because I don't want to go into explicit details. Here's just a general summary...

I seem to have gotten myself into one of THOSE situations again. I'm perfectly happy in my relationship; at least I was until about 5 hours ago. I went out dancing tonight with a group of friends. I had so much fun. I haven't been out dancing in 7 years. One of the guys recently split from this psycho chick who happened to be there. He's a really good dancer, one of very few who is able to flow and keep up with me on the dance floor. During one of the breaks it was suggested that we really ham it up and make it a real show for his ex. Boy did we ever. I can't remember the last time I had so much fun. We danced and joked around and flirted. I thought it was over when the danced ended but it seemed to me that he seemed to carry it on in the car on the way home. He kept finding reasons to lean forward and touch me to get my attention. And there was a lot in some simple shoulder touches.

So now I'm sitting here all mixed up. It's wrong on so many levels; and I know it. But I also know that I'm going to be really tempted if the chance comes up. The catch is that I've thought once or twice that I wish I'd met this guy first because he is so my type and I find him so attractive. Even if I were to split up with my boyfriend, this guy and I coulnt be together because it would cause a whole bunch of problems. It was something that should have just stayed in my head but now that it's out there I'm not sure where it's going to lead.

I'm not sure if I'm excited or scared.