The father of the Constitution called unilateral secession a "violation of a faith solemnly pledged." The commander of the Army of Northern Virginia called it "nonsense", and a insult to the memory of the Framers.
I can't understand the need for the Lost Cause cult to attempt to wrap a transparent legal fig leaf around what was nothing but Revolution. If the damnyankees were as evil and oppressive as your mythology insists, rebellion would be a perfectly honorable and moral action. You just have to show us how the damnyankees were oppressing the people of the south.
With the exception of the original 13 states, none of the states joined anything, voluntarily or otherwise. States are admitted to the Union. They don't become members unless a majority of the existing states approve their admission, through a vote in Congress. Once in the Union, a state cannot split up, combine with another state, or change their border by a fraction of an inch without the approval of a majority of the other states, through a vote in Congress. If a state needs the approval of the other states in order to join in the first place and if it needs the approval of the other states to change its makeup or borders, then it makes sense that a state would need their approval to leave.
The Militia Act of 1792, as amended in 1795 precludes unilateral state secession.
The Judiciary Act of 1789 requires that "controversies of a civil nature" between the states be submitted to the Supreme Court.
As you can see, the Federalists acted quickly to solidify the power of the national government.
Walt