In the end, the author gave us an open ended story, some might assume that they continued as "brothers", some might interpret it as being a couple and that's exactly why its open ended its up to you to draw your own conclusion of the story. It maybe bittersweet, sweet, sad, unsatisfying or anything else kind of ending that you will draw and I think that would depend on your own experiences as well as understanding as a person. Still we can't deny that the author gave us a story of love, leaving us the feeling of also wanting to fall in love.
Lol, the seme clearly stated "Take care of me, little brother", which you say when beginning a relationship. Also they promised they'd always be together, which implies they're not going to have any lovers except each other.
Some might want closure to this story and some might not.
Some might view their relationship as weird being it an incest one.
Some might be creep out.
But what can you do when he/she is the person you fell in love with? Is it so wrong to pursue that love, your happiness? How can you give up when you know your love is mutual?
Hahahahha just some thoughts running around my mind