Rob mentions Kristen in an interview with Epoca Magazine (Brazil)

EPOCA - All actors say that sex scenes are very awkward to do, you always have a lot of people around. As you and Kristen know each other so well, is it easier? 

Pattinson - Actually I don’t think doing sex scenes is weird. You know that nobody will say anything, the directors don’t want to embarrass themselves, they will not say how to do it. But it's fun to do it with Kristen, it seems kind of silly. In fact, it becomes more difficult. When you don’t know the other person you won’t say she's doing something silly, or play all the time. If you know the person, it's more risky (laughs).

EPOCA - Kristen Stewart said the wedding scene was as if she were living it. How was it for you?

Pattinson - Mine was easy. Especially in the beginning. There was so much expectation because of the dress, paparazzi everywhere that Kristen was very stressed. As she was walking to the altar, and the camera approached me, I started to get nervous because I saw how she was in shock. So I think that it needed to support and act as if I knew what I was doing (laughs).

Source - Full Interview Via @Mel452 Via @KstewAngel - Thank You!