I remember reading through most of the articles and amendments until the 12th and feel that seceding was illegal but once I start googling the question people start popping up claiming to be saying that it was indeed legal once it happened and when Texas V White happened by 1869 the Supreme Court ruled seceding without permission was illegal, so it sort of makes sense how it's legal but the constitution doesn't seem to anything written saying its okay, rather it says states can be entered into the United States but nothing of leaving is mentioned.
The post I read about is from a History.StackExchange being answered by E1Suave. Where he states that at the time there was no law saying they couldn't and I guess he also meant it wasn't specified at all whether or not it was allowed thus giving them permission.
Discussing it in terms of laws doesn't make much sense. It was a constitutional question. The Constitution was created with a process by which states could become part of the United States. It didn't say anything about whether states could leave the United States. This is one of many questions the Constitution left unanswered. Jonathon Gienapp's, The Second Creation, is a good work in terms of understanding why the constitution didn't answer questions like this.
The question of the constitution of secession occasionally came up, some Federalists in New England flirted with the idea during the War of 1812, for example, but the issue really comes up with the Crisis leading to the Compromise of 1850. Secessionists argued that southern states had the right to leave and should do so to create a republic based on slavery. The argument they made was that the states were sovereign entities who had joined the United States, so they could choose to leave. The counter argument, eventually expressed by Lincoln, was that the United States was not just a club of states, but a perpetual union of the American People.
It is interesting how strongly the argument about constitutionality of secession was advanced by secessionists. There was an easily available alternative; the right of revolution, which had a pedigree in the Revolutionary War. I think it comes down to fears of slave revolt.
Focusing on the Supreme Court decision in Texas v. White misses the point. The Civil War decided the question of whether secession was possible. The outcome of the war established the federal government's supremacy over the sovereignty of states. The Supreme Court was just officially ratifying that decision in 1869, not deciding the question.