They both have to proclaim it to be ‘married’.
There are some partners (even in male-female couples) who refuse to get married.
But maybe now the roommate can get some judge to recognize it after the fact when that person’s family comes calling for their stuff back when their relative dies.
They do NOT have to proclaim to be married. It depends on the state. If you have sex and live together in some states after X years you are considered married.