A few weeks back, I twittered the phrase "authentic sexual identity," and a couple of people disputed the very concept. This puzzled me but I guess that if they define authentic as rigid or monolithic, I agree. It's pretty clear from studies and observation that there is no unified sexual identity, neither for groups nor for individuals. So "authentic" in the sense that there is only one official version is definitely NOT what I had in mind.
What I mean by authentic sexual identity is "authentic to the person," and not "authentically categorizable for the rest of their lives." And by "authentic to the person," I mean it's the kind of sex they really want to have based on the things that really turn them on.
One of my key themes in Sex for Grown-Ups is that no amount of labeling and defining will ever be adequate to encompass fully the variations that comprise individual sexual identity. In one of the cases I talk about, I mentioned that while I knew my patient was "a submissive kinky lesbian," that label still barely scratched the surface of her sexual identity. There is no one standard model for what makes someone "submissive," any more than one can put all kinky people in one box or all lesbians in another.
To the label-inclined, those people who can engage in endless debates over the precise definition of a category of sexual identity, all sexual variations must look hard-wired. To me, sex is the opposite: it runs as much on software as hardware. Yes, there is a basic, hard-wired "orientation" (gay, het, lesbian, bisexual, trans, etc.). But how that identity will interact with the greater world over the course of its life is a crapshoot. Sexual identity itself is fluid and plastic and permeable, with waves that continually overlap and build only to wane and retreat like the ocean itself. What detritus it may bring to shore or carry away is unknowable.
Sexual identity is about nuances, variations, the little extra details that went into making you you. However you were born, your individual life experiences -- your caregivers, your schooling, your religion, your friends, your first sexual encounters -- all create tiny differences between your perceptions of sex and the next person's perceptions.
Put another way, your sexual identity is as alive as you are: it grows, it alters, it responds to emotional changes, life stresses, unexpected opportunities, hormonal swings, and changes in your health status (whether from disease, drugs or age) too.
So I don't see an authentic sexual identity as a fixed matrix. I see it as a living organism, as rich and complicated as one's personal identity, and something that can only be addressed by looking at the whole person, and not the labels others have assigned to them.