the Constitutionality of Cases where Citizens are of Different States; is this really a State Issue for Montana as in the State v. Bill Windsor? He is not even a Montana Citizen and has never Been.

Between Citizens of Different States

"Constitutionally allowed cases
“[A]ll cases, in law and equity, arising under this Constitution, the laws
of the United States, and treaties;--
all cases affecting ambassadors, other public ministers and consuls;--
all cases of admiralty and maritime jurisdiction;
--to controversies to which the United States shall be a party;--
to controversies between two or more states;-"

Source
https://www.umt.edu/law/files/ford/Ford_CitizensLawSchoolppt2011.pdf

"11th Amendment
Amendment XI

The judicial power of the United States shall not be construed to extend to any suit in law or equity, commenced or prosecuted against one of the United States by citizens of another state, or by citizens or subjects of any foreign state."
https://www.law.cornell.edu/constitution/amendmentxi