The Constitution DEFINES the Union. No state can do anything which changes that Union. The Union is defined as all those states which either ratified the Constitution OR which petitioned and were admitted by Congress.
All a state could do is petition Congress to be let out or work to pass an amendment specifying they could leave. There is NO power to unilaterally abrogate the constitution and it is not in the 10th amendment either.
You have already been shown the explicit statement Madison made in this regard.
And it is true that Davis violated the CSA constitution as much or more than Lincoln did the United States Constitution. Yet where are your complaints about that?
Don't change the subject. I am still waiting for proof that the Constitution prohibits secession. You won't find it.
Lincoln however, BLATANTLY violated it.