"The term "marriage" is religious in origin."
And the United States of America are British in origin. Does that mean the 13 colonies should have bent over and took whatever the king gave them?
Just because something has an origin in one place does not mean it should never go beyond it's founding boundaries. To prohibit something to it's origins would demand all but 13 states of the Union dissove their own existence, and every single amendment to the constitution be wholly unwritten. And, to say nothing of technology.
Get a British passport and sail your way back!