Wow, I think I can relate to you, even though in slightly different circumstances...
Recently, I had my first romantic experience ever. I had never even kissed a girl before this, I was a FA in its pure state: a male kissless virgin in his late twenties. Decided to start playing the game after years of focusing on work and career, without virtually no interactions with women (apart from conversations in a professional environment).
By omitting my FA status, my insecurities and acting confident - i.e. by being 'fake' I guess - I was able to get a girl to like me: (1) met her casually in a social gathering with my group of friends; (2) our group started hanging out with her group; (3) managed to get her attention and go out in a first date; (4) kissed her on a second date; (5) during a week or so we kept hanging out, kissing, making out, etc.; (6) finally escalating into sex and spending the night together at her place. I was too nervous to continue my acting during this last step, so I told her about my 'secret' when I felt our making out session was escalating towards sex. She said she was surprised, but curiously at the time she said she didn't mind. We continued and she asked me to spend the night with her, we kept talking, kissing, cuddling, etc. until the next late morning. The truth is, a couple of days later - and without further romantic meet ups - everything was terminated by her really fast, not even face-to-face, without any explanation. Furthermore, as she remained somehow part of our group of friends, we frequently meet each other and I seem to somehow repulse her as if I was some sort of monster, a 'mistake' or as if she was ashamed of having been seen with me.
I'm not really sad because I 'lost' her: I found it all to be a very good learning experience. What is really making me crazy is that, due to lack of feedback from her, I can't understand what is so wrong with me that caused that type of behavior from her part.