One thing that I feel was completely handled way too lightly in ATLA was the genocide of the Air Nomads, and how Aang was supposed to stop Ozai and be happy for the rest of his life.
Are you kidding me? All of his people are dead. To top it off they died horribly. And now he is burdened with the responsibility to make sure that Air Nomad and Airbending ways don’t disappear, all alone. Whether Katara’s there for moral support or not, he is still the last Airbender.