Summer nights in Syria.
I think that something major must have happened with stiles and lydia before the "you'll forget me scene." Because they're so open with each other in that scene, kind of like they're dating or have already confessed their feelings. They sure as hell weren't that open with each other in 5x19. Especially the way Lydia says "I won't." It's so emotional and open. It's hard to explain but I do think that a kiss or a confession might have happened before he is like "you'll forget me."