*sniff* Such a beautiful story! So much feeling, you made me cry!

Very nice, so much emotion. Lovely job.

I was a bit confused about the brother part at first but after realizing it was Hiccup, that makes a great deal of sense. I think Toothless would see him as a brother, as an equal and not anything less, or more because he still has his pride as a dragon.
Quite honestly, reading this, reminded me a great deal of the books and I'm not sure if you've read them or not but you hit the nail on the head concerning the conflict within those pages. Can dragons and humans live peacefully? Co-exist in the same world? It almost seems as if you have set up the beginnings of the plot to the third movie and that is something incredible in itself.
I didn't think about the other dragons questioning him concerning his and Hiccup's relationship when it was this full of tension. That is truly an excellent point. Hiccup is at a crossroads. He could choose to hate dragons for taking his family away from him yet again (since really, dragons have torn his family apart twice now though both not intentionally) like Drago or will he forgive Toothless and try to be like he was before; open to all dragons and the idea of peace?
As you read further you can feel the story build up into this crescendo of emotions and the turmoil that both these characters feel yet still in the point of view of Toothless. Seriously, this is incredible writing and you should be very proud of this. Their bond is one of the strongest things I've seen as well and I think you really expanded on that in Toothless's view by explaining not only the emotions he faces, but also the problems and criticisms he'll endure to mend the bond they have.
Only one thing. The title, is a bit confusing in some ways as it doesn't really elaborate in the story the brother that is missing. I understand it to be the old Hiccup Toothless remembers before Stoick's death but it may be a bit hazy to other readers.

You pulled this off excellently! I felt the depths of Toothless's affection for Hiccup perfectly, and the subtly lingering pain in the fact that Hiccup didn't want his comfort was so prominently there, yet I can't pinpoint where in the story it is. It's just there! A major part of the story, but so carefully woven in that it's a fixed part of the weaving.
I also love the way you portrayed the dragons. The "Nest" and Toothless's protectiveness of it was wonderfully done. It made me think about the dragons in depth.
And the interaction between Hiccup and Astrid was great. Toothless's POV of it didn't subtract from it at all. In fact, it strengthened it in that Toothless understood how necessary Astrid is to Hiccup.

This story is so beautifully done, you have every right to be proud of it! And I can't wait to see what you'll write next!:D

That was really, really good. Wow. Would you ever consider writing another chapter where we can see Hiccup starting to heal to Toothless again?