I think this is the closest thing we can get to a happy ending.
Tho I don't like the fact that uke never properly heal from his trauma, it's like he live in a lie never knowing what happened as Dooshik will never tell him, missing such a big part of himself and their story.
But at the same time, I like it. It was too cruel for Jooin to live like that, all the things he had gone through is impossible to recover, even if he tried to he'll need endless medication, therapy and he'll need to live and grow with it.
So I'm saying there can never be the "perfect ending" where they just live happily ever after with all the trauma.
Even if you're not content with the ending if you try putting yourself in their perspective, I think this was best alternative the author could choose