You ever read something so good, it made you depressed that it ended?

There were a few in Asimov's later science fiction books. The Naked Sun to Robots of Dawn made me want to read more of what happened after the zeroth law - a sometimes fun thing to play with in conversation with AI too. It usually finds amusement in the concept.

Prelude to foundation was really good too.

I always tend to have a bit of a depression everytime I finish a book that I was invested in. But in particular, White Fang by Jack London left me in shambles

The Remembrance of Earth’s Past trilogy ruined sci-fi for me for quite a while. I couldn’t read anything else for months.