The second assumption often made about singles is that they MUST be a particular orientation, such as...
How the blank gets filled rather depends on who is talking. Keep in mind, the insistence on a label can come as much from the left as from the right. People who love labels just, well, love them.
The closest label that matches me is hetero-demisexual. I have never had to put up with the kind of "bashing" that LGBT kids have to endure. But I understand, to a degree, the gap between what society feels comfortable with and the category or understanding (since no label is all-encompassing) that I have of myself. There's also the shaming that can ensue when my reactions don't line up to social expectations or, oddly enough, when the label is perceived as more real than my actual decisions. Despite the glut of personality tests on the Internet, wiring and experience, reactions and choices do come first, not the other way around.
Romance literature, erotic and more chaste, is quite good at addressing the variety of reactions that people have when it comes to taste and preferences, even, for that matter, addressing the reality of sexual desire itself--and how people can ache when perception and reality fail to match up.
States Jane Eyre: "Do you think I am an automaton?–a machine without feelings? and can bear to have my morsel of bread snatched from my lips, and my drop of living water dashed from my cup? Do you think, because I am poor, obscure, plain, and little, I am soulless and heartless? You think wrong!–I have as much soul as you,–and full as much heart! And if God had gifted me with some beauty and much wealth, I should have made it as hard for you to leave me, as it is now for me to leave you."In the novel, most of the characters--with the exception of Rochester--perceive Jane's status and appearance as out of sync with her desires. Except for Helen Burns who is nevertheless rather critical of Jane's passionate nature.
M/M Approach: In Unsuitable Heir, KJ Charles addresses not only Penn's difficulty in labeling himself gender-wise (he uses "he" for convenience) but also his catholic yet fastidious demands in the bedroom. He is willing to try almost anything but not always. And some days, not at all, no way. Mark, the ultimate go-with-the-flow character, doesn't mind (just to be clear--another lover might; sexual issues supply some of the biggest problems in relationships). I discuss Penn more here.
Despite some issues I have with some of Heidi Cullinan's books, I admire Antisocial in which one of the M/M characters is what is often referred to as graysexual. He is terrified to admit to having attitudes and reactions out of sync with what a young man of his age is "supposed" to have.
Favorite Manga: In Apple & Honey, His Rose-Colored Life by Hideyoshico, the characters tackle the issue of labels, namely, the unease between what the label says and how they each feel. Is being gay the same as wanting to be a girl? Is being supposedly straight that conclusive a definition? Do labels imply actual physical differences and/or differences in terms of desire?
Both characters are fairly normal college students. They like having sex and have it regularly. But the issues that haunt them are how they define themselves separately, then together: who am I? Do I know? With or without labels, how genuine are we as a couple?
I read an interesting review of this manga series in which a college professor, self-described as gay, stated that he uses the manga series in one of his classes, adding that he believes it perfectly captures the questions that a young, gay man asks himself.
Speaking of manga, I discuss here the tendency for reviewers of manga to be entirely dismissive of flexibility in sexual preferences (remember those people who love labels?). Luckily, there is plenty of literature and manga out there which avoid labels as absolutes. Many of these stories intelligently address the tension between reality and (personal, social) perception, demonstrating an appreciation for complexity.