No. 3 - “Time Keeps on Slipping” (Season 3, Episode 14)
Easily the saddest of Fry’s failures involving his love for Leela, this story has him finally winning her over, only to have it all snatched away in a matter of mere seconds. Storylines on “Futurama” can often be out there (even though most of the time they are actually very scientific and educational), so the plot to this one is a little complicated. But the gist of it involves the Planet Express crew gathering time-traveling particles, called chronitons, from the far reaches of space in order to age mutant atomic super babies rapidly into mutant atomic super men in order to beat the Harlem Globetrotters at basketball (told ya). However, this begins causing random time jumps, with no one remembering what happened in between. To fix it, the crew must use a gravity pump to move stars around the area of outer space where they took the chronitons from. However, the time jumps continue and we see that Fry and Leela have gotten married. Since neither of them know how it happened, time jumps ahead again and Leela has divorced Fry, thinking he must have somehow tricked her into marriage. In the end, the stars must be imploded into a black hole to fix everything. Just before the implosion, Fry sees that during one of the time jumps, he apparently taught himself to use the gravity pump and literally moved the stars themselves to spell “I Love You, Leela” in the sky. But before he can show her that this is how he got her to love him, the bomb goes off and his love message is erased forever. Bummer.