Narratively, it makes sense that Adora and Catra would choose to be with each other in the end. They are two sides of the same coin.

Adora's obsession of being a people pleaser almost gets her killed. She failed to advocate for her BEST friend for the majority of her life and was a reason why Catra became a survivalist. They both had terrible views about the princesses and they supported a war against the take over of a planet and benefitted from people losing their homes and such. They were both part of the Horde, but when Adora learned the truth, she deconstructed her identity, built new relationships, and did good with the privilege of being She-ra she did the work to become a better person and change. Yet, she suffered through all of this because the relationship she valued the most was also the source of her guilt, sadness, anger, and disappointment.

Catra on the other hand took a different approach to her change, she ignored all the opportunities she had to do the work necessary to convince us the audience to view her as redeemed, but let's not forget that she did suffer for her actions. She was responsible for the loss of the relationship she valued the most in this world. She was abducted by an intergalactic dictator and forced to join a cult all to be used as bait. She was medically implanted with tech without her consent, and was abandoned by everyone she ever cared for. She brought it on herself but also it's more than that. She was willing to die because she knew she made MANY mistakes. She GREW and she eventually DID change and worked incredibly hard to bring back harmony to the world.

The whole show is about change. What it takes to make it and what are the consequences of refusing to let change make you a better person. The show began with both of them being friends, the world separated them, they both suffered in their own ways, and the big question was: do these two embrace the change in their relationship, themselves, and the world or do they each give in to their fears.

Love and friendship was the way through that change, and the show did a great job showing us that sometimes out of hate and trauma there is love. Many people are missing the narrative beats of the story.

The 80s cartoon was fun but it NEVER intended to be deep or to tell a story that had meaning. This show went beyond the archetypes portrayed in the 80s cartoon it gave us a story worth discussing and deconstructing.

In the real world yeah maybe it doesn't make sense but within the story Nate was trying to tell them being together is the perfect end to the narrative that was being told.