I don’t believe a government mandate is necessary for this. No one would refuse a patients visitor anyway. The health care team is not their to take care of a patients morals, only their health.
Hospitals don’t turn people away for pete’s sake. People shacking up also visit each other in the hospital.
As far as decisions; ANYONE can legally designate ANYONE to make decisions for them in the event of a medical emergency. It takes 20 minutes to get a power of attorney. (faster than getting married).
Let's say a gay man is out of state and gets in a car wreck where he's in a coma. If there is no marriage who makes the decisions, relatives or partner?