So, I choose this scene because... man, I have butterflies on my stomach every time I watch her. The looks they share are amazing. Man, I think I start to ship them in that scene ♥
We know she is in love for him for a long time (like she said on pilot episode). But we can see that he is falling for her too. I think, at this moment, he's falling because he sees that he can trust her. Because she can be his support. He can found in Emma what he can't in his wife. The confidence he needs.