first off, you should really be comfortable about your sexuality. that's the thing that would make you go that extra mile. i went into that habit of masturbating in front of sexual partners when i stopped thinking too much of what they think and how they would react. i just "felt" i needed to release it. i didn't ask their permission. the first time, i just closed my eyes and did it as if i'm doing it alone in my room. i never stopped showing off ever since.
try it, girl. you won't regret it.