I would say that the 10th Amendment puts the burden on you. The amendment states:
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
Article IV requires congressional approval before a state can enter the Union, and it requires congressional approval for any change in a state. Any alteration of borders of a state requires congressional approval. If a state wants to split in two or more parts it requires congressional approval. If a state wants to join with another state it requires congressional approval. Clearly the power for a state to unilaterally change its makeup is a power denied them by the Constitution. And that should include the ultimate change of status, leaving the union. Actually, I see mention of a State entering the union – not seceding (and the example is not applicable to the first 13 States). And I see mention of state borders – but not secession. As for a State splitting in two (or four ;>), your example may again be less than absolute – consider the Texas annexation documents. In any case, although you may honestly believe the restrictions you mention “should include the ultimate change of status,” secession is nowhere mentioned in those restrictions. Nor is a prohibition of secession necessarily implied by those restrictions, any more than the constitutional age requirements for Representatives, Senators, and the President necessarily imply similar age requirements for federal judges.
As Mr. Madison noted:
"The powers delegated by the proposed Constitution to the federal government are few and defined. Those which are to remain in the State governments are numerous and indefinite.”
And Mr. Madison made that observation before the Tenth Amendment ‘insurance policy’ was appended to clarify the matter. I would suggest that the burden remains on you...
;>)
What you see is congressional approval required for every change in a state's status. But that's OK because I never expected you to accept my argument anyway. Any more than I accept your arguement that the Constitution can forbid states from acting in any unilateral manner where the interests of other states might be affected, except for secession. That makes no sense at all. Which brings us back to my original point. I can no more prove to you that the Constitution forbids unilateral secession than you can prove to me that the Constitution allows it.