I'm generally curious, also one of my favorite authors has often said, "my books all have sad endings because I believe you should leave the happy endings for real life." So whenever I read her work, I have to brace myself.
I'm going to put these in spoilers because I'm not about to be rude and spoil it for some people. But there are some obvious ones out there. Spoiler Rudy and Papa's death in The Book Thief by Markus Zusack. I literally had to put the book aside and howl into my pillow because of these two. Sirius Black, Fred Weasley, Tonks and Remus Lupin, Dobby from assorted Harry Potters. I can't read Dobby's death. I have to skip it unless I'm feeling particularly vicious to myself and then I'll read it without being able to see it. The scene where Harry's walking through the forest at the end too makes me inconsolable. And finally, the dog's death in The Art of Racing in the Rain by Garth Stein. Holy shit that one knocked me out of whack forever. Absolutely stunning book. Oh... and for some non-fiction: Paul Kalanithi, the author of When Breath Becomes Air died from cancer. It was expected, but I still felt a bit empty after reading it. He wrote it in such a way you felt like he was going to recover and pull back and make it. And then his wife wrote the epilogue. Gah. Now I need to go stare out a window as it rains and reflect on life.
Which author was that, Aella? So I can avoid her... If real life had more happy endings, I might have agreed with her. But after seventy years, I no longer expect them on a regular basis. It's nice when they happen, though ... IRL or in fiction. But to answer your question, I think that the death of Boromir in The Fellowship of the Ring came as a blow to me, although Tolkien presaged the hell out of it.
The death of Déagol at the hands of Sméagol (Gollum). Though it goes unnoticed within the lives of those in the rest of the narrative, it is the first bell struck in the final drama of Middle Earth, the beginning of so much doom. What I find exceptional about the use of it narratively, is the parallelism between Déagol & Sméagol vs Frodo & Sam. It begins with avarice and murderous treachery between two hobbits. It ends with unshakable love, faith, and friendship between two hobbits. I know that doesn't sound terribly emotive and tragic. Written fictional narratives rarely "hit" me in that way.
It's a tossup between these two: Spoiler: The Dark Tower Series (Also King) Eddie. God damn you spent books making me like him. Spoiler: Oryx and Crake (Atwood) Oryx. Okay, this one might actually take the cake. I still think about it. Edit because poor memory.
I was going to say 'Old Yeller' as well! From childhood books: the death of Matthew Cuthbert in Anne of Green Gables. Maybe it's childhood, where death doesn't seem quite so 'normal,' that makes these stand out. I mean, remember the death of Bambi's mother in the movie? I know adults who still claim they never recovered from this shock. Adults who happily eat venison whenever they can get it. Oh, and Steerforth, in David Copperfield. He's easily the most interesting character Dickens ever created, in my opinion.
Gandalf? I mean, he didn't die die, but I was 10 at the time and highly erratic emotionally. Not like now when my heart rate never goes above 7. Back then I freaked the fuck out.
Johnny from The Outsiders. Nowadays it's hard to get a tear from me with a novel, but Johnny dying had my middle school ass sobbing. Saw the movie in High School and that brought back the pain. Can't forget Lennie from Of Mice And Men. Yeah he accidentally killed that girl, but being a brother myself, I cannot imagine how hard killing him must of been for George. It was either he do it or the crowd of angry townsfolk would've lynched him. Sad sad book.
I don't really get upset by books as an adult... but I was a little bit hit in the feels when J-Hawke gets fragged pretty much by accident in Matterhorn by Karl Marlantz. As a kid I was upset when the sheep dog dies in Susan Coopers "The Grey King" The only time I actually draw a tear these days is in my own writing when a main character I like has to be killed for plot reasons...I figure that's good because it might effect the reader the same way
A few people already said Old Yeller, but that one will always be the saddest death in a book I have ever read.
Lots of those were really sad for me too. Old Yeller was the saddest. In the last book in The Fifth Wave: Spoiler I'll add Cassie.
Spoiler Augustus Waters in the Fault In Our Stars ... and Bruno and Schmuel in The Boy In The Striped Pyjamas
I'm going to sound like an utter dork for this, but Achilles reflecting on his own death in The Odyssey is still something that makes me emotional. 'Do not speak such high words on death to me, Odysseus. I would rather be a slave above ground than lord over all the breathless dead down here'.
I quite literally flipped the last page in The Song of Achilles by Madeline Miller just now, not minutes ago. Spectacularly romantic, constantly flushed with fingertips grazing godlike cheekbones and pectorals, Patroclus the envy of every human who draws breath, the flutter of tent-flaps under Anatolian stars where a mortal prince and his demigod lover shake the foundations of Troy with their passions. Not bad. ETA: The end is rather rushed. The book is told from the POV of Patroclus and focuses quite intensely on his romantic (in this take) relationship with Achilles. We know there is much more story to come, but the narrative POV demands we cut off just after Pyrrhus (Achilles' son) enters the narrative.
Ted's suicide in The Go-between. Probably because I was an impressionable teenager when I read it, and thought I was in love with him. It looks like Old Yeller needs to go on my 'to read' list.
I haven't read Old yeller, but did see the movie. A tear-jerker for sure. But there was a book called Bristle-Face, about a dog, that I read in grade school where we actually sat and read in class (only the once I think). I don't actually remember if the dog died, but part of it was incredibly sad. The class bully unfortunately sat very near me and saw me sniffling and tearing up and brought it to the attention of the whole class. Good times.
In Gates of Fire, when Spoiler Alexandros dies above Thermopylae. That scene sure hit me in the feels. Hell, the whole book did.
The death of the kestrel in Barry Hines' Kestrel for a Knave - immortalised in the Ken Loach movie "Kes" if you think of individual iron filings as things that have depressed you over the years, that scene is a big magnet stuck into a pile of them - comes out covered in the buggers and many of them you can't just shake off. Boo. Good thread, but I wish I hadn't remembered that scene )c: