Ethan Rickover - Monk
Major spoilers if you haven't seen Monk because it's not until the very last episode do we discover that Judge Ethan Rickover was person responsible for murdering Monk's beloved wife Trudy.
Jadis - The Walking Dead
Jadis calling a helicopter to rescue Rick proved her redemption was real but also took Rick away from Michonne. Will Rick and Michonne ever reunite? We can only hope the upcoming Rick Grimes movies will provide answers.
Guy of Gisborne - Robin Hood
Robin Hood defeats Guy of Gisborne and lives happily ever after with Marian -- right? That's not how it plays out in the BBC version. Instead, Guy stabs Marian, and she dies in Robin Hood's arms.
Kaylons - The Orville
Watching Claire and Isaac fall in love was very sweet. A more bitter discovery was finding out Isaac's people intended on exterminating all organic life, and Isaac betrayed his crewmates in the process. He eventually realized he couldn't turn his back on The Orville but not in time to prevent the fracturing of his and Claire's relationship.
Shawn - The Good Place
Every single time Eleanor and Chidi remember/realize they're in love with each other, Shawn and his minions wind up doing something that erases it from memory.
Sin Rostro - Jane the Virgin
Sin Rostro faked Michael's death and fried his brain to induce amnesia. Years later, Michael and Jane reunited, and he regained his memories. However, while Michael and Jane still had feelings for one another, they realized their paths in life had diverged too much for them to go back to being husband and wife.