A Farewell to Arms
Futurama Season 9 Episode 2 (06/20/12)
While trying to retrieve Fry's only pair of pants, the Planet Express crew discovers a hidden pyramid with an ominous message written in ancient Martian that Amy translates: the world is ending in 3012. Thankfully, the pyramid is a handy spaceship that can hold 30,000 people to escape to Mars. All of Earth's luminaries (and Scruffy, the janitor) are allowed on board, including Fry, but Leela is not allowed on board. So, in a gesture of his love, he sneaks her on the plane with his identification.
Unfortunately, this winds up being very bad, as Amy's translation missed that the apocalyptic event was actually meant to happen on Mars, not Earth. Mars spirals around the solar system, briefly coming within proximity to Earth for those on Mars to escape, but with Leela stuck because of a broken leg that was Fry's fault when he tried to help her earlier. Leela decides to trust Fry one more time, but he fails to save her, though Scruffy the janitor was able to. Leela is touched by Fry's willingness to keep on trying to help her in any way he can, even sacrificing himself, even if it winds up with her worse off for wear because of it.