After Hollyhock, BoJack's half-sister finds out that he got a teenage girl drunk and then just dumped her at the hospital with alcohol poisoning, she starts to avoid him. Finally, after the disastrous, second TV interview she sends him a letter, one which Bojack really dreads to open.
When he finally does,
Bojack is absolutely shattered and starts drinking again.
We never know (in-universe), what was the content of this letter, but has there been any hint given by producers/directors/writers etc?
Of course, we can roughly guess that she tells him
to never see her again
or something similar, but the letter seems to be quite long and it would be great to know any details.