The Constitution only provides for the addition of states to the Union. It does not provide for secession. The Supreme Court ruled, in Texas v. White, 74 U.S. 700 (1869) that the Constitution is therefore a contract - binding on all parties unless ALL parties agree to dissolve it - and just as one party cannot unilateral tear up a contract one state cannot unilaterally secede from the union.
Yes, but those same courts twisted the intent of the 14th Amendment to include children born here illegally as citizens.