I know of no one who would deny two men, or women, who wish to bond themselves together the right to do so; to be considered next of kin, joint owners of property or accounts, co-equal partners in all things.
There surely is a way in the law to accomplish this.
It is a reasonable request.
But, to demand that society change a universal, miilinial old institution that is rightfully considered the foundation of any nation, is not reasonable. It is petulant.
Many things change over time, some things never change, and never will.
The 'Nuclear Family'; man, woman and child is the surest way to perpetuate a civilization. In that setting a child learns by observation how the two sexes live and relate to their fellow beings. It works pretty well.