Since each state is sovereign (wherefore we each live under 2 constitutions), each state which in principle is prior to the union of states…
(Some States having been creations of the Union of States having had no prior existence as any sort of separate entity.)
“…has proper authority to secede.
Sometimes, but the other parties to a compact may be justified in requiring one attempting to break the compact to hold to the compact or suffer a penalty, provided these other parties have not broken the compact themselves.
It is not right (nor anywhere prohibited by the US Constitution)…
I don’t believe the US Constitution is relevant to this.
…for the one aggrieved (or allegedly aggrieved) state to be at the mercy of the those that broke covenant.
Your position kind of breaks down there. You went from if the contract has been violated, written above, to those that broke the covenant without any substantiation for the transition. Those who broke the covenant may be the ones who did so by leaving when the others are not at fault.
According to you, those who violated the contract cannot be judges of the case, so if those who violated the contract are the ones who broke the covenant by leaving when the others are not at fault, they cannot be judges of the case.
And of course, each side is likely to say the other side is the one in violation. Each side is likely to take the position that the rights they have under the compact/covenant/agreement are just. There will be a real or perceived conflict of rights. Absent a sufficiently organized society, and there isn’t one at this point in part because, as you say, there is no judge or higher authority to turn to, such conflicts are settled by consent or by superior force imposed by the party who is willing and able to bring superior force to bear.
It's not the position that breaks down. It is the political reality. The difficulty is with perceived violations and grievances. What seems to be unappreciated by those who take your position is that the perceived grievance must be very significant to wish to commit to so dangerous and difficult matter as to break off. Indeed it is possible that those who broke off 'broke covenant'. True, and that, my friend, is the entire problem and the reason for this debate. Practically speaking, if consent of all is required, secession is never going to happen. The alternatives to my position are only these: chaotic revolution or enforced union. Therefore, the Framers never included in the Constitution requirements for secession.
Regarding your statement about the 'creation' of new states. It is the people of each State who create each, the US acknowledges their existence and admits them with the same standing as the other states. That is why I used the word 'principle'.
To conclude, on your side, you do not fully recognize the sovereignty of the state (or rather the people in each state). Now I don't demean the Constitution as a mere treaty. However, if the violations are severe enough and irreconcilable by other means, secession is not a mere option but a duty. What, then, you ask is severe enough? I respond that it is to be determined by the people of the state? The question is when do violations become insufferable? Now some will suffer more, some less. As for individuals, so too with state's. That is why I prefer to leave it entirely to states. Of course, I consider it unlikely one State would secede on its own.
Part of the reason I continue this discussion too is that I've also been considering other obstacles and implications in secession, which is good at least to consider even a little, if not thoroughly.