Vincent has seen a lot, so whatever he sees here must be pretty darn shocking for him to register this look of utter amazement. Even Cat looks concerned.
Cat: Bright side: In the meantime, we get to fall in love with each other all over again. Vincent: What makes you so sure we will? Cat: Cause we don't have a choice. I told you - we're meant to be. Vincent: You really believe that, don't you? Cat: I do. And you do, too. You just don't remember it yet.