Well, I'd seen the gonorrhea quote all over the place, even before I'd read the letters, so I assumed it was real and reflected Fritz's disillusionment after winning (I was also operating on a version of events where he used his power as king to poach Heinrich's page/bf), but now having read the letters more closely instead of just going "...what?" and giving up, I have NO idea whether Fritz is maybe making the gonorrhea thing up. It would sadly be in character from him as a prank/power play.

One day we will solve the sordid mystery of the two brothers and the one Marwitz. (Whatever else it is, it is obviously sordid.)