The archetype of the androgyne
This is not well known, but actually, transgender people have been discussed across the planet in many many societies, and mostly they are understood as people who have special insight into the difficulties of self-identity, and in most world mythology, androgyny is a mystic idea, signifying the paradoxes between opposites. This novel makes Sydney try to teach Jonathan about moving past "right and wrong" do to what's best for one's self. That fulfills the archetype.
The motif of passion
It's easy to say, "You can't just do everything you want!" but actually, Sydney consistently shows how in his life, listening to his emotions helped him to move forward in life, as the novel's title suggests.
The allegory of the parent and son
There's a crass Larkin poem to this effect, but basically, no one gets out of childhood without some serious mental damage from their parent(s). So therefore, one of the most relatable stories in human history involves a son asking his parent (father/mother?) why they did the things they did, knowing that it would cause suffering. Sydney's answers are honest and compelling, but still so beautifully human, because after all, parents aren't God, they're humans. It's easy to think they were supposed to be perfect.
The allegorical absent father
One of the main conservative criticisms of same sex marriages between women is that a child will be raised without a father, but as Jonathan well knows, people don't just have one gender inside, they belong on a spectrum, and ironically, Jonathan ends up working things out with a dad, essentially. Just like Hamlet or Simba, he wants to know what it means to do the right thing - here, in the absence of Sydney's example.
The "Fortress of Solitude" allegory
Superman was also raised without his parents, and when he encounters his major existential crisis, it is by working on himself under the instruction of his father that he overcomes his failures and shortcomings and creates a real superhero out of himself. This is essentially what Jonathan is doing too, except that Jonathan is visiting Trinidad instead of a Fortress of Solitude, but he does still enjoy almost 9 years of solitude with his (now) trans-father, hopefully to the same effect.
