the first few dates are supposed to be the honeymoon period where each person is usually on their best behavior and what not, so for this chic to be acting the way she did on your first date, heaven forbid how she will be treating you after a month or two of dating when the honeymoon period is over and she feels that she can let her hair down so to speak around you and then show you the real her..
you've only been on one date, so i'd run forest run.. you don't owe her anything, but if you'd like to, you can simply say that she's not the person you thought that she was or don't think that things are going to work out ....
but it sounds like if you invest anymore of your time into this relationship, only bad things are going to come from it.. if you're not interested in a bi female, just make that clear at the beginning of a relationship.. i have a gay friend and she doesn't like to be with any girls who have recently been with any males, so your feelings are not too out of place in the gay world, believe that much..
and i agree, just because you're gay, doesn't mean that relationships should be any harder to come by than a none gay person, of course it would all depend on where you live and all, but that is no reason to settle for the first gay person that you've met that has taken an interest in you either.
in a year or two, you will be laughing at the thought that there is no one else out there for you other than this pill head chic..
the thrilse of live
love you too sweet heart 
