Why do you want him to be something he's not?
Why do you insist that he change to fit your ideal?

It does sound as if he's got some sexual issues he needs to work through...But if you aren't willing to work WITH him and be supportive of HIS choices, then maybe you two shouldn't be a couple.

I've had people try to change me to be their "perfect" partner, and it just made me feel worthless and unwanted and resentful. I tried to change, but then I wasn't myself anymore. I can't pretend, and I shouldn't have to.

Nobody should have to pretend.
Why can't you just accept him the way he is?
Either that or let him go free to find out who he really wants to be.