This is based on opinion. Please don't list it on a work's trope example list.
Tearjerker / The Sound of Music
Baroness Elsa Schneider in the stage musical telling Max that the Captain doesn't know that he's going to propose to her, and they sing a sarcastic song about how typically "lovers have to struggle" and there's no challenge when two lovers are rich. Come a few scenes later, the Captain starts to develop feelings for penniless and lower-class Maria.
The children are so depressed after Maria leaves.
Baroness Elsa Schneider breaking off her engagement to Captain Von Trapp in the musical, because he won't agree with her to bend to the Nazi ways. Although the Captain's Love Epiphany about Maria follows, it's a gut punch since she does have feelings for him and politics rather than Maria breaks them up.
Rolf's Face–Heel Turn, poor Liesel just couldn't understand why he was acting so coldly towards her, even when she tries to flirt he coldly tells her "I'm now occupied with more important matters. And your father better be too if he knows what's good for him!"