Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Tear Jerker: Night World
Keller's note her mother left with her:
People Die... Beauty Fades... Love Changes... And You Will Always Be Alone.
Delos's back story.
Poppy's whole story. She goes from the highest of highs—a funloving teenager enjoying her first day of summer vacation and having a new-found resolve to finally get with James romantically—to finding out that she has pancreatic cancer and won't survive the summer. And even though James offers her the chance to save her life, this also means never growing old or having children, and she can never be with her family again. It's something that she struggles with throughout the entirety of Secret Vampire, even after becoming a vampire.
Special mention goes to when she calls home after waking up from conversion. Her parents think she died from her cancer. And she sits there in tearful silence listening to her mother's voice. She desperately wants to say something and tell her mom that she's alive and she's okay, but she can't bring herself to do it.
Ash's Character Development throughout Daughters of Darkness. When Mary-Lynnette tells him she killed her childhood friend and werewolf, Jeremy, in order to save him, he becomes increasingly upset and apologizes over and over again. In the finale when he has to leave, he keeps repeating "I wish I was human" as he says goodbye to her.