Lexa realizes she has feelings for Clarke - The 100
Lexa had been making heart eyes at Clarke for quite a few episodes, but it was during this scene that her feelings seemed to come together. If she didn’t already have an internal realization when questioning Clarke about Bellamy, their kiss later on in the episode made everything crystal clear.
Mark realizes he still loves Lexie - Grey's Anatomy
To be fair, Mark never stopped loving Lexie. He had, however, moved on and didn't say "I love you" back when she did. But when Lexie was fatally injured in the plane crash his feelings for her became crystal clear.
Amy realizes she has feelings for Jake - Brooklyn Nine-Nine
We know from Rosa that the double tuck is what Amy does when she likes someone. Right after she had an adorable conversation with Jake, the tuck happened after he left the room.
Chidi realizes he loves Eleanor - The Good Place
When Eleanor handed Chidi a tissue before he sneezed, he was a goner. Michael told her that the act of Eleanor anticipating Chidi's needs is what made him fall for her. It may seem like an odd time to realize you love someone, but for Cheleanor, it makes perfect sense.
Barney realizes he loves Robin - How I Met Your Mother
No one could have guessed that when Barney's life flashed before his eyes the only thing he saw was Robin. Whatever feelings he had tried to repress for her were brought to the surface and Barney knew at that moment he was in love.
Cheryl realizes she has feelings for Toni - Riverdale
It's no secret that Cheryl wasn't Toni's biggest fan. But the two had an emotional conversation at the diner and Toni understood Cheryl in a way that no one had before. Thanks to Madeline's excellent acting, you can see the exact moment Cheryl fell in love.