I never really understood monosexual people and I'm becoming increasingly convinced that they don't understand themselves.
I'm all for identifying however you want, but maybe reconsider your worldview or self image if you're identifying with something so explicitly contrary to what you're doing. Or at least don't act like confusion is unwarranted.
As for your questions,
Sexual orientation is not a lifestyle but society makes it difficult to not accommodate a minority sexuality with lifestyle choices. The sheer volume of repulsive behavior and aggression queer people are subjected to by cishets makes it an easy choice to only associate with other queer people.
Of course this isn't always possible, and it becomes harder the more visibly nonconforming you are.
Gender is a construct. So are traffic lights. If you ignore either of them, you get hit by cars. Which, also, are constructs.