And I am sorry you are so thick, please do both of us a favor and read Maine's existing Constitution, you don't have to read it all, only the preamble Article One sections one and two. If you still don't see our authority to secede, then please go bother someone else, for you are hopeless.
It does not matter what Maine's Constitution says.
Why?
Because everything it says is ultimately subject to federal review.
What actually matters is what the US Constitution says.
Any luck on those statistics regarding the 300,000 new immigrants you'll need?
Also, any word on how your private army of 12,000 poll enforcers will be able to violate federal law on June 12, 2018 with impunity?
Or how your referendum will make it onto the ballot in the first place?