I was really surprised when I saw the previous comments and ratings, I think this manga doesn't have the recognition it deserves.
I can understand all the critiques about it being too short and confusing, but the fact that not all the questions are answered (so the short lenght) isn't a problem to me, on the contrary. What I like in this manga is that a certain mistery is kept up, and the accent is put on the encounter of the characters and what they go through to recognize their love.
It's the way that counts, not the ending, and so I don't find this too short or lacking development. The unanswered questions allow us to imagine how things could be (like for the reunion of the brothers), and tha'ts something I appreciate though it's not often used in yaoi mangas, and besides that, I think the plot is developed enough to not leave us unsatisfied.
I especially liked how in the first story, Nana was able to go ahead even though he still doesn't remember his past. I also liked how the emotions are not always overshown, which leaves enough space to see things from the character's point of view.
What is really great about this manga is the characters' development, which is subtle, delicate, realistic, sweet, and endearing. It's like a candy you enjoy licking bit by bit with delight. And what's more, the artwork is beautiful and very sweet. I just regret a litlle bit there isn't more hot stuff, but it's not very important in this case.
So, it's true it may not be the usual type of shounen ai / yaoi, due to this way of treating more the characters than the plot, but it's very well done and it's actually what makes it interesting in my opinion. So I really recommend this to read.