WARNING: The following contains major spoilers for Rick and Morty Season 4, Episod 8, "The Vat of Acid Episode."
When it comes to dating girls, Morty is predictably inept. For the entire series he's been trying to get with his schoolgirl crush, Jessica, to no avail, and whenever he tries to win her heart through Rick's science, it doesn't go well. However, in "The Vat of Acid Episode," Morty endures his most tragic love story. He doesn't need any science tricks to get into his first real relationship, despite having a helpful device. Instead, his love is broken by Jerry.
The beginning of the episode sees Rick and Morty attempt to fake their own deaths in a crystal deal gone wrong by jumping into a fake vat of acid. The criminal creatures are traumatized by the brutal "suicide," and they stay where they are to ponder their feelings. After hours of waiting under the fake acid and trying to prove they're dead, Morty loses it and shoots all three creatures.
An angry Morty rants to Rick that his acid idea sucked and hates that he never listens to his ideas. Rick shoots down Morty's idea of a "do-over" remote, but his grandson questions if he could even create such a device, so the egomaniac scientist creates the "do-over" remote, which allows Morty to pick a "save" spot in time, which means he can return to said point if things go haywire.
Morty does everything expected of a teenage boy with this kind of power, but that soon changes. Suddenly a dialogue-free sequence occurs right after Morty hits save on the "do-over" remote and opens the door of a coffee shop for a girl. With no other science or technology used, Morty and the girl hit it off.
What transpires is a montage that highlights their romantic relationship. It has the same peaks and valleys any serious relationship would, from meeting the parents, to growing distant and arguing, to reconnecting and going on a big trip. Throughout the time, Morty occasionally checks his "do-over" remote, but he decides not to change anything.
Things take a left-turn when their plane breaks in half and crashes in the middle of the mountains. The remote in his bag flies to the back half of the plane, and Morty lands in the front half miles away. This romantic experience becomes a nightmare as Morty, the girl and a couple of survivors try to live in the freezing cold, eating shoes and frozen bodies.
Morty even attempts suicide, but he changes his mind when looking into his girlfriend's eyes. He's determined to get to the back half of the plane and fights off wolves and the cold to make it. Just as he reaches the craft, he passes out and is about to freeze to death, until a helicopter rescues him and the survivors.
When Morty awakes in the hospital, he sees his girlfriend alive and well. The couple's survival becomes a national news story, and it feels like the two are destined to be together forever. That is until their 'Welcome Back' party, where Jerry knocks over the TV remote.
He looks over and sees the "do-over" remote in Morty's bag next to him, thinks it's the TV remote and picks it up. Jerry tries to adjust the TV by clicking the "go-back" button on the remote, and all of the sudden Morty is right back where he started from, the moment when he first sees his girlfriend.
Instead of doing exactly what he did the first time, Morty panics and rushes to the girl. What he's saying isn't known, but he's probably telling her about the relationship they just had that no longer exists. The girl is confused then horrified when he touches her face, pepper spraying him in response.
After the ordeal, Morty use the remote to save to this point, and he attempts to go back to over and over again, but he keeps going back to the moment he's pepper sprayed. Just like that, the best relationship Morty has had seems to be erased from history.
The distraught Morty goes to Rick, wanting to return the remote when his grandfather reveals that it technically wasn't a tool for time travel. It was a trans-dimensional teleporter. Every time he hits the reset button, an alternate universe is created with the consequences of the decision. Instead of having every Morty killed so the main Morty could live, he decides to have all his misdeeds converge in the same universe. Hundreds gather to arrest him, and ironically Morty fakes his death in the same vat of acid as the beginning of the episode.
Before he jumps in, Morty's girlfriend pushes to the front of the crowd and attempts to stop him, but Morty doesn't see her and proceeds to dive. The Morty she knows disappearing like this is probably for the best, considering he's also in the same universe where he committed hundreds of crimes. It also turns out that it still isn't Morty's main reality, and Rick takes him to his real world after faking his death. For Morty, at least he can use this experience to find real love in his life.
Created by Dan Harmon and Justin Roiland, the second half of Rick and Morty Season 4 airs Sundays on Adult Swim. Seasons 1 through 3 are available to stream on Hulu.