SO-OCD: isn't this just denial?
It is a fair question, and it is exactly the one the OCD wants you to spend your life on. The two can be told apart, and a therapist comfortable with any outcome is the person to do it with.

It is the question underneath all the others, and it is the one that makes people hesitate to call this OCD. What if it is not a disorder? What if I really am what I fear, and calling it OCD is just the most sophisticated denial available? Wouldn't a person in denial say exactly this?
I take that seriously. It is a fair question. It is also the exact question the OCD wants your life spent on, and I want to draw the distinction properly, because it can be drawn.
What working out your sexuality looks like
Someone genuinely working out their orientation is usually drawn towards an answer, even a frightening one. There is a pull: attraction, curiosity, a sense of something that fits, alongside the fear of what it would mean. The question, however hard, has a direction. And when the person gets to an answer, the answer tends to hold, because it was reached by moving towards something rather than away from uncertainty.
That process is real, it is often painful, and it deserves room. If there is genuine exploration underneath what you are describing, that is worth having space for, and you would need a therapist comfortable with any outcome, which is what I intend to be.
What SO-OCD looks like
This theme is characterised by wanting the question closed and being indifferent to which way. There is no pull towards an answer, only a dread of the uncertainty. The person is not drawn towards the feared orientation; they are terrified of it, and equally they cannot rest in their current one. Every test produces an ambiguous result. Every answer, however it comes out, expires within the hour, and the doubt reformulates. And the theme runs in every direction: straight people fear being gay, gay people fear being straight, and the symmetry shows that the content is not the point.
A person in denial is avoiding an answer they can feel. A person with SO-OCD cannot feel anything, because the checking has abolished it, and is running tests to find out what they are, which is not something tests can tell you.
Why the question cannot be settled by more thinking
You could think about whether this is denial or OCD for another year and get nowhere, because the thinking is itself the compulsion. Reviewing your history for the crush at fourteen, the dream, the thing you once found funny, and weighing it, is mental checking. Researching what the signs are supposed to be, and finding that every list fits you and does not fit you at the same time, is reassurance-seeking with the internet. The question "is it denial?" is the doubt in a new outfit, and answering it feeds the same engine.
How assessment tells them apart
Telling the two apart is a normal part of assessment, and it does not require you to have decided before you arrive. I look at the shape of the doubt rather than its content: whether there is a pull or only a dread, whether answers hold or expire, whether the tests produce evidence or only more tests, whether the question runs in one direction or every direction. That is a question with a usable answer, unlike the one you have been asking.
And I will not be running my own quiet assessment of what you really are while you talk. A lot of people with this theme have been holding the possibility that a therapist would take a view, and it is usually the thing that stopped them coming sooner.
What treatment has no view on
This treatment has no view about what your orientation should turn out to be, and it will never try to steer it. Conversion practices are unethical, harmful and rejected by every UK professional body, mine included. Nothing in CBT with exposure and response prevention for this theme is aimed at what your orientation is. It is aimed at the testing, so that the question of who you are is allowed to be settled the ordinary way, which is to say not constantly re-opened.
Some people finish therapy certain of their orientation, and some finish comfortably unbothered by the question; both are fine. If you have been stuck on whether it is denial, there is more on how I treat sexual orientation OCD, and the distinction is drawn in the first conversation, not before it.