Marriage is the change of legal status. It grants certain rights
and responsibilities.

Examples are useful;

Robin was in a motor vehicle accident.
Pat, whom he lived with, had no authority to make
any decision as to his treatment. She was a stranger
in law. His brother was contacted as he had the authority.

Joyce lived with Sam for many years.
Sam died.
Sam was married but his wife had left him years
ago, he never made the effort to divorce her.
The Wife got everything.
Joyce got servant wages for the fifteen years
she had lived with Sam.

Eric lived with Ann in a house left to her by
a grandparent. Her name alone was on the title.
Ann decided to get rid of Eric.

She sold the house, and took everything, even
items Eric had brought into the home, and moved
away while he was at work.

Eric had no rights and had to resort to criminal
law where he would charge Ann for appropriating
his property. Ann claimed he had given her these
things. Eric got nothing.

George and Mary lived together in his apartment.
He told Mary to leave. She refused. He brought
in his new girlfriend, and together they threw
Mary's things on the street.

She had no rights.

Hence marriage is a method to insure rights...

The right for Pat to decide Robin's treatment.
The right of Joyce to inherit.
The right of Eric to the property.
The right of Mary to security.

Marriage does not insure love, fidelity, companionship
or even compassion. Marriage only insures that a
party has locus standi in issues effecting property
and rights.