You're arguing that in cases where it is a confirmed medical fact that a married couple can never have children, that such a marriage should be desolved by the state. You're full of it.
Not in the least.
Marriage is a broad based institution that exists to protect people who could potentially create and raise children, i.e. a man and a woman, and to protect those children. It is an elevated status that represents the special responsibilities of that social unit. Society has this broad institution because it's a big picture concept.
If a tiny percentage of people are unable to produce children, they shouldn't be punished for it. Doctors have known to be wrong, and they could wind up with a child. They could adopt, and raise a child in a male / female family unit. The potential for healthy childraising still exists.
This is fundamentally different from a group of sexual hobbyists who are by definition unable to procreate, and on the whole could not raise well adjusted children. No matter how big or small a picture you look at, gay society does not reproduce, and has no need for an institution that protects children.
If they want to 'go steady' then that's fine. Behind closed doors, it's their business. We shouldn't have to finance it, or give it our sociatal stamp of approval.