Hello Scientia. I had similar problem recently. I'd always thought that I was bi but for some time males seemed to be unattractive to me at all. I thought I was lesbian. I couldn't figure out it for a long time and I finally posted at another forum.. And what surprised me is that many people don't even agree with the term "orientation" and claim it doesn't exist. I learnt the orientation is fluid and everything may change. Sometimes you like a man, sometimes you are attracted to a woman. There is nothing wrong.
Now I completely agree with that since it helped me to accept myself. I don't identify myself with any orientation. I find girls attractive, I had one encounter with them, but I do love my man and I would never change him for any girl. No need to mention men. You will just meet that person. And if you love him or her, does it really matter what sex is that person?
And I think if you were asexual you wouldn't get aroused, but I'm not the expert. It's just what I think about myself, I have also had such doubts.