I had to choose no to my spouse watching me masturbate for two reasons, 1) I RARELY do and 2) IF I do I'm very self-conscious about it. I know.
I love, love, love watching a partner masturbate in front of me. Whew! Not only is it sexy as hell, it also offers insight into how and where she likes to be touched.
"My partner (19m) and me (19f) have masturbated a few times in front of the other one. I find it amazingly hot and extremely sexy to see him.