Yes, thank you, that doesn't happen often enough.
Robert E. Lee clearly anticipated by your citation and quotation, that the dissolution of the Union would lead to Civil War, that the North would fight. He was correct in this. There have been lively discussions about how the North, initially iffy on the subject of secession, came to its determination to fight, but I think that there were two factors that determined the outcome: a) Lincoln successfully baited Davis into opening fire first, which galvanized Northern opinion and essentially transformed secession from a political movement into a war, which IMHO was his objective all along -- even before he ran for office; and b) the Northern money interests recognized the danger to their own interests entailed in the departure of the South from the Union, and they spurred as much action as they could, IMHO, in the direction of retrieving the Southern States by force.
Lee was correct in his statement that the South was exercising its natural right to revolutionize its affairs. He was incorrect about secession, and he was in error to prefer the intentions and opinions of the Founders to the sovereign voice of the People: vox populi, vox Dei. Either the People are sovereign, or we're all just kidding ourselves and we can just take it to the house.
The People acted correctly in convening conventions and scheduling plebiscites to determine whether to secede: such a determination was ultra vires any State's legislature, since they and all the officers of the States were bound by the Supremacy Clause to support the Constitution. An act of the People in their aspect as Sovereign, assembled in convention or in their voting precincts, was something else again, and I think Lee missed the distinction.
He also erred in using the quote, "perpetual union" -- that phrase is found in the Articles of Confederation but does not appear in the Constitution or its Preamble.
Correct, the phrase "perpetual union" is conspicuously absent in the Preamble, but the concept is retained by the phrase "... secure the blessing of liberty to ourselves and out posterity."
Correct me if I am wrong, but did not the US Supreme Court site the Preamble in the Texas vs White (1869) decision, using the phrase "... indestructability of the Union ... "? (I believe the context of that decision was to abbrogate any and all actions of the secessionist Texas government.)