If the SCOTUS votes to keep TFG on the ballot,

[Caliman73]

19. SCOTUS decisions are made when cases are brought to them.

Yes, there has to be an injured party. In this case, the State of Colorado took Trump's name off the ballot, the Supreme Court of the State affirmed the decision, and Trump, being the injured party, appealed the Colorado decision to the Supreme Court based on multiple arguments including contesting that he engaged in insurrection AND jurisdiction issues.

Same sex marriage was codified by the Obergefell V Hodges decision which incorporated the 14th Amendment's Due Process and Equal Protection clauses to say that licenses granted in one state for marriage, had to be respected in other states.