After the incident with Mr. Jellybean, Morty is beyond traumatized.
He knows Rick is the only person who would understand, yet the old drunken man still acts unsympathetic. This drives Morty to make a rash decision with a few choice words.
After wards Morty waits for Rick to pick him up in the middle of math for some high sci-fi whatever but remembers what he said. And guesses it's probably best they part for a good while anyways.
After all, Rick only cares about himself.
After dozing off in the middle of class, Morty slips into a very, VERY vivid dream.
One of his house.
And his best friend.
But he's gone.
Because of the toxic words.
Morty finally sees how much Rick actually needs him..and how much he needs Rick.