My life as the "OTHER WOMAN"

So I just found out I was the "Other woman." How does that work you ask?  Well I will tell you.  I have been on a two dates with the same guy.  I had fun.  I had hope for something more.  We even kissed. I know that that doesn't mean we were in a relationship.  We weren't. So how does this make me the other woman? Well apparently he was dating another woman for some time.  They dated off and on.  It was not super serious from what I gather because she lived out of the state. He did like her however and even had a former Facebook profile pic where he claimed they were friends in the comments. In the meantime we were set up and had a pretty decent first date.  He asked me on a second date...a few weeks later.  It was good. We ate dinner, watched a movie and made out. I tried to go with the flow and let him take the lead.  We texted or FB messaged a few times back and forth, but always with some time in between.  He even contacted me within the last week. Last night I found out he was dating this other girl and has been for a while.  Honestly, I am not upset at him but at the situation.  Who wants a romcom experience where you are a negative supporting role? I wasn't that into him really because all I got was a text every once in a while. That is lame.  I was pretty much over him anyway because I didn't think he was that into me with the lack of contact. But I hate that he turned me into the other woman. He was just keeping me on the back burner in case his main dish didn't quite turn out.  I don't like being there.  Now how did I learn this--well a person I work with is a sibling of the girl this guy is now dating.  It showed up on Facebook and now I know.  And because of the situation I asked my coworker if his sister was dating someone.  Yes, I did that! We have had conversations in the past about her because she is in my same boat...you know the one where you are over 30 and single boat. I know she was upset he was dating other girls. My coworker said so. I would be too.  She was just hoping for the best, as we all do. I hope for the best for her and for her future.  She after all is a girl after my own heart...she is over 30 and single.