The season finale of Rick and Morty saw the title duo return to The Citadel, and the show wasted no time in having them come face-to-face with the villainous President Morty. It's then his grand plan is finally revealed; it turns out The Citadel was created to provide an infinite number of Ricks with an infinite number of Mortys across countless alternate realities.
The Ricks created a "Central Finite Curve" that separates the dimensions where Rick is the smartest person in his universe from those where he is not. That means we've only experienced part of this show's Multiverse, but the Evil Morty finally destroys that wall and accesses a new reality (his portal gun is yellow rather than green, confirmation he's about to visit new realities).
That's where we leave that Morty - something tells us his story isn't over yet - but the episode also ends with Rick and Morty finally working together; that and the destruction of The Citadel and Central Finite Curve are a strong indication the show now intends to move on from the toxicity in the relationship between the two leads. Their fate, however, is currently unknown.
Still, it's certainly interesting to think about what this partnership could mean for the series, but it's some earlier revelations that shed even more light on who Rick Sanchez is as a character.
You see, it turns out that both his wife, Diane, and daughter, Beth, really were murdered by an evil Rick. That put Rick C-137 on a path of destruction that saw him hunt down every possible version of himself he could find in order to find the one responsible. Ultimately, he was convinced to form a truce, and it was then that The Citadel was created making C-137 a founding member).
Rick ended up landing in a reality where Beth was still alive, and that's pretty much where the series began. However, his daughter is dead, and there is no Morty in C-137's reality.
Needless to say, there's a lot here for future seasons of Rick and Morty to address...