For the purpose of this story, is it that Newt knows Grindel!Graves isn't real!Graves because he met Grindelwald before (and knew they were) or met Graves before (and knew they weren't). Because I'm just thinking how amazing it would be if it was the latter and Newt is angsting about his soulmate's possible identity.... And in the subway scene, he's just thinking "please no, please no" as he casts Revelio to confirm what he dreaded. And Grindelwald's wry expression just saying "not what you dreamed in your schooldays" and Newt just feeling all conflicted and shattered as they lead Grindelwald away....