masturbating

So my boyfriend and I had sex tonight he asked me to play with myself. I used to be very shy about it but he has asked me multiple times to do it that it's sexy. Well tonight when I did it he pulled out to cum and I continued to play with myself to get off and he just started to laugh so I instantly stopped. I have no clue why he laughed and he told me he had no clue why he laughed either. Any others have an experience like this? Am I doing something wrong?