Well, if he's "spying" on me, then I wouldn't know he's there, so there wouldn't be anything to be turned on about.
However, I do love the teasing element of my SO watching me masturbate and seeing how long he can hold off before he pounces. I find mutual masturbation very hot, too. I also enjoy being restrained, so I can't touch his cock, while he masturbates very close to my face and/or gliding his cock along my lips. Drives me crazy when I can't touch.
So, in today's lesson, I do enjoy being the observer and observee in all kinds of masturbation fun!
If you haven't, you should read this award-winning story. Fine, fine, I only won a potato, but I'm sure you won't be able to
peel your eyes away from it.