[Non-Sequitur]

Where in the Constitution is the anti-secession clause, again?

There isn't one. But while secession itself may not be illegal, unilateral acts of secession as practiced by the southern states are.

[Tax-chick]

But while secession itself may not be illegal, unilateral acts of secession as practiced by the southern states are.

What's your source for that? The Constitution is the authority which governs relations among the States, and the Constitution is silent on the matter of States' seceding.