Blood Traitor

"It doesn't matter," he said simply, all those years ago. "Nothing can tear the two of us apart, even if it means turning our backs on everyone else. It can just be you and me – Sirius and Regulus, us against the world. No matter what happens, you will always be my little brother."

-
It became apparent, after a few years had passed by, that this would never be the case. Anything could tear us apart, we would not turn our backs on everyone else. And, most importantly, it would never be the two of us against the world.
We will always be brothers, but we will never be family.