This is a conversation I had with multiple persons. At first I thought sexual orientation was strongly related to one's life-style and social background. Recently some science essays and Red Thread Games changed my mind. Have you perhaps read the whole "My Kian is gay, ok!" thread on Steam?
Well at a certain point RTG intervened with a very strong message, saying how Kian was born gay. They said you dn't decide to become gay, you're born with it. It's in your DNA.
Who am I do go against it? I'm definitely no scientist. So I accepted it. At lease fot the TLJ saga, right?
So, again, it's a body thing in that any TLJ character is born with this orientation in his/her DNA.
From what I understand of the science that's been done on this, they've found out that people are almost certainly born with their sexual orientation. But they haven't been able to figure out if it's determined by the environment in the womb, your DNA or if it's essentially random. Likely it's a very complex interaction between all of these things. Just in case you're interested.
It makes sense to agree that your sexual orientation is just part of your body in the TLJ universe, though. I think that's a good interpretation.