Again, you are more focused on him when he is bringing this on himself. So I say it again, what is the big deal if she does and doesn't want to say? Like do you even hear yourself about why this guy is so focused on his "sanity" from hearing something but being told another? And then having an obsession with it to the point that he is so focused on it, his sanity is in question?

Dude, why are you so obsessed with her playing with herself? YOU are making it s bigger deal than it is, so what if she does, LEAVE IT ALONE. So what if she denies it, for whatever reason she doesn't feel comfortable admitting it. You're being a bit extreme thinking about ending it just because God forbid she doesn't want to tell you she's playing with herself.