Well, Lee was an officer in the United States Army at the time of Fort Sumter. He resigned from the United States Army, and then fought in another army against the United States Army. I think that makes him a traitor.
You would be correct, and he had his citizenship stripped, and wasn't a US citizen in his life time. That is history. He did get his citizenship back though in 1975, as it was southern Republicans that were trying to change history. Also a lot of these monuments were propped up long after the civil war during the civil rights era, to create a false narrative of history. It was a way of saying this isn't over and that some day "the south shall rise again". I put that in quotes because I didn't just come up with that on my own. We've all heard it, and that's because many believe it. Losers of war don't get to have monuments of honor, and they shouldn't. The south lost... and that's the real HISTORY.