The point is literally in the last chapter dude, there's no "resolution" to trauma, often you'll live your entire life fighting with it one way or another. The author note says it verbatim "As long as you are alive, there is no such thing as a final curtain". Tsubasa and Kaede will have to live dealing with their triggers but that doesn't stop them from being happy. I don't really understand what kind of ending you'd like for them.
I would like to see an ending with both of them accually being happy, last panel with Tsubasa was with her frightened face, while mc was speaking with his inner demons. I would love to see them moving forward and actually be able to live good life with their trauma.
But in this ending there is non of it, Tsubasa is scarred for life, and because she was sheltered her whole life, she won't be able to live normal life without a lot of help from both friends, family and for sure few shrinks.
On the other Kaede is still scared of girls.
So are they rly happy as u said? Nope, not even close.
I might belive Kaede could be somewhat close, but Tsubasa is broken like never before.
And that's why I believe after this new arc we will see more of her, because showing us her dramatic situation, and end her story after that would be rly weird.
I think the point is they give each other a peaceful farewell. They are still moving forward and trying to find their own happiness, both mc and the girl. happy ending isn't really something you can described like having a partner whom you love and love you back.
For me, their happy ending would be able to live with their trauma with the help of their friends. Even if the trauma is still there, they know they can continue to live better as each day pass as trauma isn't something that can disappear even if it doesn't bother you as much.
For them, maybe being able to live with their own way without having to be careful something might trigger their trauma is a happy ending. Not fully a happy ending they want but a happy ending they need
So what? Now we will have different mc, but what about previous one? And what about Tsubasa? It looks like she is fighting with her own trauma now, mc somewhat healed and started to have different perspective on his situation, but even so, the way it was shown to us was underwhelming to say at least.
I rly hope we will see both of them again, because they still need their closure.