C is now married with children and holding some sort of public office and is politically on the rise. G does not know any of this. The memoir contains liberal drug and alcohol abuse, as well as several unreported crimes, quite a bit of dirt on both their families, and would out C. G took photographs documenting the entire summer because at the time he wanted to be a photographer, which he would like to have included in the book. It's also relatively sexually explicit. It would be enough to smear C's career and (probably) ruin his marriage.
Even if C's real name or even the name of his and G's hometown were not used, the details of C's personal life (his brothers and sisters, his runaway-dad and his older brother's suicide) as well as the photos would probably be enough to identify him to anyone who knew him personally.
C would refuse any contact with G, barring a forced personal confrontation.
So, legally, what can G disclose? What names, if any, would have to be replaced? What would G's editor say? What about the photos?
Thank you in advance, and if you have any additional questions I'll try to answer ASAP.