The arguement of choice vs nature is varied and deep.
I think it's both, because it makes more sense to be naturally attracted to something/someone and then make an action based on that attraction. When that comes to sex it is just a normal as when it comes to reading a book you like or watching a film you enjoy, though also like your preference of people to be around and ideas you find acceptable.
Part choice and part natural draw, because you must choose to follow the draw.