James Longstreet Timeline and Summary

Longstreet receives news from the Confederate spy, Harrison, that the Union Army isn't too far off. Longstreet is surprised and takes Harrison to Lee.
That night, before the first day of the battle, Longstreet sits out of the soldiers' poker game—he stopped playing after his children died. He chats with Arthur Fremantle, the English observer, and Generals Pickett and Armistead.
After the first day of battle, Longstreet sees that Lee's plan to try to seize the high ground on the second day is flawed—but he's unable to do anything about it. He ends up talking to Fremantle and shocks him when he suggests that the Confederate Army is not using the right tactics to fight the war.
Lee tries to convince Longstreet that his battle plan is sound. Longstreet doesn't really argue and agrees to fight, but he definitely isn't convinced. His troops are bested by the Union soldiers, including Chamberlain's, during the attack on Little Round Top.
On the night before the third day of the battle, Lee says that he wants to attack the Union line with Longstreet's troops again, this time at Cemetery Ridge. Longstreet disagrees verbally this time, but Lee's course is set. Longstreet is frustrated and sad, because he knows it's going to end disastrously.
And it does end disastrously, as Pickett's Charge turns into a bloodbath on the third day. Afterwards, Longstreet tells Lee that they now "have no Cause." They haven't lost the war—but the course for their eventual defeat is clear.