Date Me, Date My Girlfriend?

A friend and I went to a pub to hang out and shoot pool - don't ask.

We were sitting at the bar, making small talk with the bartender and a tall, dark and handsome gentleman walked up beside me. We began talking about stuff like travel - mainly because he noticed I was drinking a Limoncello - and Italian lemon liqueur. He said that not many people who had not been to Southern Italy would know about the drink, blah, blah, blah...

So, toward the end of the night, we exchanged numbers, and me and my girlfriend went on our merry way. He called the next day, asked me to lunch the following week. I accepted!

We had a GREAT lunch. Talked about a variety of things. At the end of lunch, he seemed a little hesitant - which was very awkward because the entire conversation we had beforehand was non-stop, good interaction. He looked at me, and said that he wanted to know how I felt about dating two people at once. I said that I didn't think it was a big deal, since I am fairly open about my relationships and if I was dating two men at the same time, I was doing just that - DATING.

He hesitated again, but smiled as he said, I would like to date you. I think you and I would have great, fun times. Needless to say, I was flattered. Handsome man, asking to date me - forget that I didn't know anything about him - it was nice to know someone valued my time and sparkling personality so much!

Then, I realized, that dating him could mean a number of changes to my so-far-so-good single life. In the briefest of moments I took to begin pondering that, he then says, "of course, I would like you to meet my girlfriend." I looked at him and began to laugh, "What?" I chuckled, "Girlfriend?"

YES. GIRLFRIEND.

Apparently this guy has a girlfriend who he lives with and with whom he has a Poly relationship with - see Poly Amory. In other words, he loves more than one person at a time - see Mormon.
He wanted me to meet his girlfriend so that we could see if we hit it off. If we clicked. I asked "Why would it matter if I got along with your girlfriend?" He then began to explain that I would actually be dating the both of them.

I am sorry. I know I have not dated in a while, but is this for real?
He was completely serious.

Why can't I just meet a NORMAL guy?!?!