He is going to make himself very welcome at that and steps right behind her so that he can lean in over her shoulder, leaning his head into hers a little bit to clearly express some of the romance in their relationship. Why? Well, he thinks it'll be easier to warm Steve up in this way and he waits for her to take the photo.

"Can I type out the text?" He asks curiously leaning against the wall after before taking the phone. He dictates it once he's done typing. "Isn't she the prettiest thing you've ever seen? -B" he says not hitting send and handing the phone back over to Natasha.