Personally, I think they will be together years later (meaning being real lovers).
Now, they have amorous feelings for each other and they accepted that fact but the progress of their relationship is very slow. But, Yutaka is still young too.
I think they are in no hurry and are taking time to completely accept their relationship and to make it evolve.
they definitely share a special bond that isnt normal for siblings (meaning they deeply love each other) but they also cant have a future together.well maybe the can if they leave for a place far from their town or mother.its not a tragic end but not a happy end either.at least they both feel the same way and is not an one side-love.
What? It obviously is a happy ending.
If this was real world and not a manga, yes, "they can't have a future together", but it was clear that they end up being lovers, not just only because of they last conversation (in which obviously the big bro asks the little one "if he's ok with him" not in a brotherly way haha) but also because in the last chapter there's a page that looks like the fridge of their home in which is also a photo of them togethere.
This means they left the town to be able to live togethere as lovers. How is this not a happy ending? :D
I don't get it... Are they together or aren't they?