Fantasy come through

My girlfriend and I have been dating for two years for now, everything is cool we both work have cars nice place to stay and most importent of all the sex life is great.
We went out for dinner the other day for my birthday had good dinner and wine, after dinner she asked me if I had any fantasys I would like to talk about, I told her that I would like to have a threesome, she said she was okay with that, she told me she can post an add on a dating site and let me know with the responds.
Next day she called me at work and said that she found some one and she is going to arrange for us to meet at a hotel room and this is going to be my birthday surprise, so right after work I got home picked her up and drove to the hotel and checked in a room and waited for my special person to arrive, I was very excited, the door knocked and when I opened it, a man at the door said " I am your birthday surprise " Oh boy talking about a surprise I was not expecting a man it did not across my mind.
I walked out on her and never seen or talk to her again that was two days ago.
P S just be careful what you ask for.