Sara and Snart - DC's Legends of Tomorrow
Snart made the ultimate sacrifice by giving his life for his friends. It tore Sara apart to leave him behind, but she kissed him goodbye, knowing that she had to respect his decision.
Helen and Nikola - The Sanctuary
Planning to blow up the sanctuary and sacrifice herself for the greater good, Helen kisses Nikola and sends him away to safety.
Cheryl and Toni - Riverdale
This was more of a "locked up and being mentally abused" situation than a physical life or death one but the stakes were still high. Toni breaks into the Sisters of Quiet Mercy and kisses Cheryl before they make a grand escape with the guards on their heels.
Chloe and Clark - Smallville
With danger all around them, Chloe realizes she may never see Clark again. She grabs him and kisses him goodbye before he goes to face Zod.
Clarke and Finn - The 100
Most people aren't a big fan of this couple, and we can't really blame them. They had a pretty bad relationship based off of cheating and lies, but we do have to admit that Clarke loved him. Ultimately, Finn ends up sacrificing himself to be tortured by the grounders, but Clarke kisses him goodbye and gives him a quick death instead.
Stiles and Lydia - Teen Wolf
With Stiles dad about to be sacrificed in an unknown location, he starts to have a panic attack. Lydia tries her best to help him breathe through it, but when that doesn't work she kisses him. We wouldn't recommend actually kissing someone in this situation, but the distraction caused Stiles' breathing to return to normal and created an absolutely breathtaking and beautiful moment between the two.