Thank you for your question. I know it must be confusing to try to understand where your feelings come from and how that might affect your life and relationships. Let me start by saying that your situation probably is not as rare as you might think; many people who consider themselves heterosexual are attracted to someone(s) of the same gender – most people do ponder the idea of homosexual/bisexual relations once, if not numerous times, in their lives.
That being said, I think it is also safe to say and confirm to you that labels do not matter at all – except when they make you feel better . It might be the case that you were legitimately attracted to this girl, but that it will never happen with another woman. Conversely, it might be the case that you could potentially be attracted to multiple women, given the opportunity. It is hard to know whether your attraction to this woman was just alcohol/fun or genuine physical attraction, since you had never been in that kind of situation before.
In my opinion, you should ponder the possibility of being with a woman physically. I also think that if you have not already done so, you could perhaps bring up the issue with a close friend (only if you feel comfortable of course), because sometimes sharing your feelings with someone who understands can truly alleviate some of your concerns. I truly believe what matters in life is that you feel fulfilled, whether it be never being with another woman, or trying it once, or even trying it multiple times!
On the other hand, how do you feel about your fiancé’s behavior and interests? How do you think he would react it you told him about your attraction to this girl? You say he is turned on by girl-on-girl situations. Does this make it easier or harder for you to express sexual attraction and maybe even have, eventually, a physical sexual/romantic relationship with another woman? These are all questions you could ask yourself before discussing this with your fiancé. As long as you stay true to your feelings and honest with your fiancé, and that he in turn remains open about sexual encounters you might have, I think you could allow yourself to experiment with this side of you.
I hope this helped… Please write back if you have other questions!
Cat, for AlterHeros