Our first act as a nation was to REBEL against the authority of the Crown, not secede. Please get your terms straight.
Actually when they rebelled they were not a nation, nor even 13 separate nations. Separation (secession?) did not occur for over a year after the rebellion started. The Declaration of Independence was an act of secession however. The difference however was the the 13 states/colonies had no legal sovereignty before separtion, the states of the Union are legally sovereign, in all but a limited number of areas laid out by the Constitution. You'll note that the list of limitations on the states is much shorter than the list of powers granted to the Congress, which is still quite finite. Neither the limitation nor the powers would seem to prohibit, nor give Congress the power to prohibit, peacefull secession. (The shooting didn't start until after secession in 1861, and was initially more a case of local overzealousness (by Citidal cadets in at least one case) and by a local militia commander in the critical one rather than an act of official policy of the state in question, South Carolina, or of the Confederacy. The states all seceded separately, as individual acts of their legislatures, spread out over some time. Lee for instance was serving in the Federal Army and stationed in Texas (San Antonio) when Texas seceeded, but he did not make his decision to turn down command of the Union Army, and take command of the Confederate one, until his home state of Virginia seceded some time later.
BTW, I would like to see the source and context of that January 1861 quote from Lee.