What hurts the most is that the people we saw at the end were not really Aziraphale and Crowley as we knew them. Not with all their history, memories, and everything they had survived together.
Yes, the ending does make sense for their characters. They would never have been truly happy while Earth continued the way it was. They would never have found real peace in a world that kept forcing them into the same pain over and over again.
But at the same time… it still feels unfair.
After everything Aziraphale and Crowley went through across time, after seeing them at their best, their worst, and everywhere in between, all of that history is suddenly gone. Their bond, their pain, their growth, their memories: erased in a blink.
All of their memories are gone. 6000 years of love is gone.
And yes, the idea is still beautiful in a way. No matter the universe, no matter the version of reality, they will always find each other. They will always be drawn back together and choose each other again.
But it still hurts, because the two people at the end are both Aziraphale and Crowley, and also not quite them.
They have the same souls, the same pull toward each other, maybe even the same love. But they do not carry the full weight of the history we watched them build. And that is the painful part.
They got their happy ending, but they lost the lifetime that made that happiness feel satisfying.